Go far far away, and don't come back, nor call, nor write...
If you can forgive your sister, you can forgive your boyfriend. It doesn't necessarily mean that you should stay with your boyfriend. Cheating is cheating and if that is not acceptable to you, you should find someone who will respect that wish.
You either forgive her or leave her.
No. Get away from cheating drug addicts you're better then that.
First ask yourself if you really want to forgive her.
he's not cheating on her, but if he was she'd probably forgive him as long as he doesn't do it again.
Yes, he can forgive if he truly loves her. You might be able to start a whole new relationship.
Definitely not. If your fiance is not sincere with his apology, there is absolutely no need to forgive him or her. You may leave him if you wish.
Forgive and forget !
That is a decision only you can make.
Becasue it is hard to forgive and forget
Yes you can. Forgiveness is part of every true relationship.
you shouldn't because he came back for you to make you feel worse