Why was she upset? It's not like she was dating him when you starting getting involved with him.

So you stole him from her and don't feel bad about it? Hopefully you will still be happy when someone steals him from you. No integrity on either of your parts.

Did I follow that correctly? Her ex-boyfriend is now your boyfriend? If so, your final sentence sums it up well.

Are you still with the same guy, or with a new one. I don't judge you. Sometimes no one can stop attraction. You should stay away from her. Maybe she's holding a grudge and she will never trust you.

Well, you made your choice. Maybe she will get over it someday but if she has any sense of pride, she wont bother.