Please answer Honestly i really need honest answers right now! 10 PTS!!?

i am seriously flirting with this chick that has a bf in my college, the thing is it is very obvious she loves my company i make her laugh and i listen to her she shares intimate stuff with me to show how close we are. the choice now is that being a nice guy i am torn between stealing her from him cause i fell like i am ruining a couple or something plus they've been together for over a year. BUT we are so compatible like we just flow, there is no effort to impress the other is like this natural likeness is just there, and its making me really want her more so what do i do? HONEST ANSWERS WITH GOOD REASONS BEHIND THEM! 10 POINTS!!!.