Ok I'm 29 and my GF is 27 and we've been exclusively dating for three months now. We have our ups and downs like everyone else. We do however tend to get in petty arguments and sometimes they blow up bigger than they should.
I put blame in our conflicting communication styles and most certainly some insecurities on both of our sides.
I advice you to checkout Marshall Rosenberg's Non-Violent Communication seminar on youtube. It speaks about getting in touch with one's needs as well as hearing the needs beneath another's words; extremely effective tool for any relationship, particularly for the one you have with yourself, first and foremost. The "insecurities" comes from an ambivalence in conveying your needs to each other and to see them as 'gift' opportunities rather than as criticisms or faults on the other.
But for the most part it's been pretty good so far with the potential for LTR. I'm a confident man that knows his boundaries when it comes to a relationship and privacy.
With that being said, I had a total lapse in judgement this past weekend. I was sick and hopped up on meds and me and my girl were kinda on edge due to a little argument we had but we planned to spend the whole weekend together.
"Lapse in judgment" = intuition in this case. I wouldn't chastise yourself over this, your intuition is working perfectly fine, your concerns just weren't brought to consciousness so you rationalize it as you having done something wrong and likely feel guilt as a result, ironically. I'm not saying I agree with the behavior, but you did it for a reason.
We just planned on relaxing because she was a little under the weather as well. We had a good Friday night, cooked dinner and chilled. When it was time to go to bed I couldn't sleep because the meds had me all hopped up. She fell asleep and for some reason beyond my comprehension, I impulsively grabbed her phone uggggh. Honestly I've never done this before!
She has given me no reason to suspect any cheating but I do have some trust issues from past relationships.
From what you've shared, I'm not entirely convinced of that, and I'm pretty sure you aren't either.
I was open about my insecurities and we both felt it wouldn't be an issue. So I go through her texts and lots of threads from guys and definitely some flirting. There was even a picture of a Martini and a caption saying "waiting for you" to some guy. That was from, I think, the day before where she never mentioned she was getting drinks. She didn't lie but I was unaware that she was at happy hour. There was another text to a pastry chef where he showed her a picture of a cake.
She responds "I want that!" He responds "me or the cake?" and she says "both 
" Like WTF! I have to say we did break up for about a week a few weeks back and I don't remember the timestamp of that conversation.
This looks like the case of a 27 y.o. (presumably grown) woman who doesn't know how to conduct herself appropriately/set her own boundaries with men. We don't know her intent, but it's not a good look. My last gf was doing something very similar, and in fact I'd peer into her FB and texts every once and again and often found what I was looking for. Not good, and I can guarantee your checking behavior will only increase. Bottom line, there's a lack of trust and safety in this relationship
I know she has a lot of guy friends (and gay friends) and is very sociable because she plays in multiple bands and needs to get people to shows. There were a few other texts that seemed off but I don't want to take things out of context (even with the two examples I've given). I finally check myself and stop looking but I'm obviously infuriated and hurt for two reasons.. 1. that I even violated her privacy in the first place and 2. what I found. She eventually wakes up and can tell I'm not happy. I try to play it off but we start talking. I never tell her that I looked through her phone but like a conniving person I became that night, I started asking her questions related to what I saw. It didn't get anywhere and I eventually dropped it. I truly try to let it go and we sleep close to each other.
You had immediate needs that couldn't be ignored (need for safety/security, and the need for trust both which you didn't have in that moment). You can convey that to her (and this is where Non-Violent Communication helps immensely) in a non-aggressive way. "I feel sad and anxious when my partner engages with guys who are flirting with them. I would feel more secure in this relationship if she have some stronger boundaries with the opp sex (define what those boundaries are, while being reasonable about it)", for example.
The next day we are cool but that is all I'm thinking about and it's just consuming my thoughts. She's around me so I can't truly process everything either. We don't fight but are definitely distant from one another. I blame it on that I'm sick and we just carry on through the day.
Obviously you're feeling unsafe around her.
That night I can't sleep again and like a freaking idiot I go through her phone again. I see she deleted those two conversations that I mentioned (I'm assuming she picked up I knew something was up). I was out on my porch doing this and while I'm still looking she comes out and asks where her phone is. I play dumb and say it's in my room even though she thought she had it in her backpack. I go in before her and place it on the ground by the bed and she eventually goes in and finds it. I continue to play dumb but doesn't seem like she believed me. She wants to leave and I'm just feeling odd emotions I've never felt before because of my immature and uncharacteristic behavior. I tell her we need to break up because of all this arguing and being uncomfortable. She says ok and leaves. I send her a couple petty texts and she says "hope you found what you're looking for in my phone" I deny again and that was that. I text her the next day to call me but she says there's nothing to discuss so I leave it alone.
Passive-aggression never deals with anything, it only perpetuates and gets further away from the root of the issue.So you're wanting her to mind read and figure out your needs and meet them; won't happen.
Now before I possibly get berated for invading her privacy.. I fully understand what I did and am ashamed. It was a total lapse in judgement and an isolated incident. I've never done it before and I will never do that again. And to anyone else reading, I urge you to not do it as well. You never find anything good and your mind will play tricks with what it sees. Sometimes there is shady things going on (which might be in my case) and sometimes a text from a friend or even a gay friend can be taken out of context and interpreted incorrectly. And if you suspect foul play in a relationship then odds are it's doomed. I didn't expect foul play and have pretty good intuition. That is what is confusing me about my behavior.. why did I look??
Is your mind really playing tricks on you? Or did you just find what your body was telling you all along? You're going through a lot of cognitive dissonance SPAM because on the hand you went with your intuition/gut, but on the other you feel you've done an injustice to the relationship by breaching the trust, which likely was never there to begin with or you wouldn't be in this situation.
Now I'm just not sure how to approach this. I don't know what to believe about the texts and I don't know if I should tell her I looked and confront her about it (that is if she will even talk to me and discuss it). Do I continue to deny? I feel if I come clean that will be the end because I invaded her privacy. If I deny, I'm not sure if she will believe me. I made such a stupid mess and at this point just want to make sense of it and move forward one way or another. I really do love this girl and don't know what to do. Any thoughts? Comments? Suggestions??
Have a frank discussion with her about your needs, and what those unmet needs are in the relationship from the frame of how the two of you can build this together as a team, not as a "you failed me, now you better fix it" mentality. I'd go listen to some NVC before anything.
CHAT
