When I first met my gf she had been with her bf 2.5-3 years... ended up being 5 years, a ring and an engagement party. Throughout this time we were awesome mates. It got to a point where I wasn't happy simply being the boyfriend without the benefits - I was always the one talking with her about her problems, giving advice, we were out together most days, every wkend etc. So I just removed myself from the equation, stopped hanging out or talking to her at all.
Now it's been almost 6months, she's asleep in my bed as I type this.
I had reservations about how things happened and how quickly we switched gears. Mainly because I didn't want to be the rebound guy. I knew what I wanted, I wanted her to be sure of what she wanted. I think we lasted maybe a week of giving it time.
I don't regret anything that happened, I don't think I stole her from another man. She left of her own accord for her own reasons.