i have a little drama with my best friend's boyfriend?

[Kaydie]

so her boyfriend and i are pretty good friends. well he flirts w me alot but tries to stop himself..but he just told me he likes me. he said he wished he had "talked" to me first and that i was gorgeous and all that...well i automatically was like "i have to tell my best friend" but heres the thing...she has gotten played by every single guy she has been with...she gave up hope then this guy came along and has given it back to her. and he does really like her and has no intentions of cheating on her. she is the happiest i have seen her in a really long time and i would hate to make her go back into her depressed hole and not trusting anyone but me. I dont know what to do. if it were me of course i would want to know...but i asked her a few weeks ago in a 20 questions game if she would rather be happy and not know her bf cheated or know he cheated and be happy and she said she would rather not know...and its kind of a similar situation. should i tell her or not???