I will be brief. A girl with boyfriend (not a so serious relationship, they've been together for 3 months but they dont see each other cause she is in an erasmus in my country) showing a lot of interest.
However, one day I talked about her bf. I asked how does she manage to keep a relationship at a distance/aloof, and well summing up, basically it is like if I qualified her for being loyal. Ok... gargantuan boner hahaha. Since that, she always uses the excuse of her boyfriend when I try to advance or to ask her out, when in before she didn't. There has also happened other things besides that one that may have affected this change of behaviour, but I am interested in this one.

Why do you guys keep talking about their boyfriends?
You made him real. You brought him into the foreground and yes, now he's there. At this point the bf is not an excuse, it's a reality. She didn't do it before because an interested woman will not be mentioning a boyfriend to the man she's interested in. For obvious reasons.
That however doesn't hold if YOU do it in her stead.

By the way, you mention a gargantuan boner because she's a loyal girl.. but want to get her to cheat?

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Yes I screwed up doing so haha. And yes I want her to cheat. Because 1)they were together only for 2-3 months. And 2)at the begining of everything she told me "Well yeah, But well now I am here (she is an erasmus) and he's there. So idk what will happen" she told me something
Like that in a tone of voice that was expressing "It is not that important. I leave the door open to you".
Maybe I missunderstood that sentence and she was not really meaning so, but well.. after all,she would not keep texting me if she really wanted to get rid of me and be loyal. (That's my reason number 3)
I mention a gargantuan boner because it is like I rewarded her for being loyal (I didnt explicitly said so, but it is like I subcommunicated it with that conversation that we had) So, from my point of view, she may be acting hard to get and using her bf as excuse to not seem a slut to me.
And 4) she was showing interest before I did the boner
5) she only mentions her bf as excuse after that conversation...

So yeah, I want her to cheat with me. I don't find it unethical in this case.

I wasn't questioning the ethics I just find it weird that you seemingly appreciate loyalty while trying to get her to be disloyal.
Not entirely sure what you mean by rewarding her though.

Playing hard to get isn't a thing. When a woman is swept of her feet she doesn't start playing stupid games that risk fucking it all up for the sake of.. of what?

She's simply not interested enough. She may have been. She may have been looking for an excuse, a 'one thing led to another' or overall a light, fresh adventure. But that fantasy pretty much shattered when you brought the boyfriend into the picture.

I know it sucks to hear, but you can't unbreak glass. You can however not break it in the first place, so next time, do that.

PS: Being perceived as a slut is of concern when sex is an imminent possibility. You're not at that stage yet.

_________________
I know my place. It's me on top of the world.

My in depth texting & dating guide.
There's no such thing as shit-tests.
How to keep a girl.

Rewarding is like qualifying.It can be either you find something you like about her and you express it, or you keep being interested and asking questions about something that she likes.

I didn't explicitly say that I liked that she was a loyal person.
It's just that I read that in order to reduce the shields of a woman with bf it is good to talk about her bf and to say things like "Oh so it"s going to be a relationship forever, you're gonna marry and so on.." so yeah. We can see that it didn't work that well.