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.
She should be put on your "watch list" immediately.
NO
Apologize, and if he's your true, he'll forgive you.
Of course he should! Why wouldn't he forgive you for jus being out? He can always see you another time..
It's up to you to decide what to make of it. If you felt like he was letting you down, then you should say so. If you feel like he had a good reason for forgetting, then you should forgive him.
she should really apologize and ezplain why she did that and eventuallly he will forgive her
Tell him the truth. If he loves you, he will forgive you. If he doesnt forgive you, he is a bad bf and you should break up.
If your boyfriend sincerely wants to be forgiven and you can forgive him, take him back. If he doesn't want to be forgiven, he doesn't love you any more and you should move on. If he does want forgiveness and you can't forgive him, then your relationship is dead and you should find someone else.
You should have known that he didn't love you when you found out that he cheated on you.
No, he/she is not a good boyfriend/girlfriend. Leave him/her and wait for him/her to come crawling back!
You have to find this answer yourself. No one here has the information or experience that you do.