Yo, I can totally relate to your story, im experiencing the same thing so imma type out what I think and hope you find your answer, and if you do please let me know
So basically same story except after one time I asked her if she's playing games with me? She said no and I just tried to kiss her, but she didn't want to and told me she likes someone else and I was like , alright cool then, I accept the fact that I tried and it didn't work. Done. Now im gonna do what you did and totally freeze her out(Done it many times before ) and usually most girls (sometimes 1 month sometimes 1 year) will send a message in some way, like i miss talking to you etc, and then i'll be like yeah cool, okay, ok, bye. Like I totally don't care and im comfortable with myself after what she did(or didn't do..). Get my point? in your case just say be like" I really like you yeah, and wanna be friends, but I just cant tolerate the thought of you being with someone else, so thats why i'm doing this. Wish you the best of luck. " Something like what the dude in the 2nd post said ,except explaining why (that you cant see her kissing someone else).
Goodluck bro
Edit: How you're supposed to act with her around? Just be yourself and have fun.. Show her that you're having fun without her, and believe me when I say she will miss you more and more and want you more and more

. When that happens and she signs that she wants you, its your time to think if you still want her, or if youd rather be with someone else that doesn't play games.