I'm actually the guy she is cheating on her boyfriend with (so not exactly your question, but hopefully close enough).

So far it's just emotionally, but we get closer and closer to crossing the physical line all the time, and I'm not sure how things will end. Whether we will cross that line before they break up or not. But that's the thing, they will almost certainly break up. And to be honest, I think all three of us know this. It's a dying relationship, but none of us are willing to finish it off.

So in the mean time she spends most of her time with me. We talk and hang out, play league of Legends (which she loves, and he won't do with her), watch Netflix together... In a lot of ways I'm basically already her boyfriend, it's just not "official" yet.

I do feel bad, because her current boyfriend is a nice guy. She actually flirts with me more than the other way around, and even talks about being my girlfriend. I'm sure if I wanted to, I could have her, but I don't want to do that to her current boyfriend. Even though it's obvious they aren't going to work out, I don't want to be the cause... At least not directly.