My bf has trouble showing his feelings because of the past he can be really nice to me but can change his attitude in min. is something wrong w him?

Probably: In a certain sense, guys do not show their feelings as well as gals do. This might just be some relationship-building/trust issues still need to be worked on. However, if he pathologically swings from loving to abusive in a short time, then i would remind you that there are 150 million other men in this country that you could go out with. No hitting or domestic violence allowed! if so, get out!