you're very vague about your situation...so i dont know how to respond

I mean in like--how to rebuild trust and stuff like that...how to make it better.

Give him some time.Guys are different from girls.Girls are open and completely emotional where as guys keep to themselves.It depends on how long you've been together and if your sure that there was a point that you are positive that he loved you back.Because if he does,then he cant get over you just yet.Dont push him or do anything crazy or to annoy him. Love makes you do crazy things.You need to true to yourslef and apologise and the people you have been bad to.Once you believe you are really a good person(i hope u are)then eventually he would see a change and forgive you.If u really love him then you would be willing to wait.If he gets with another girl,it means hez on the rebound and is trying to forget about you which mean he has feelings for you still and cant control them by being on his own. Dont feel hurt and dont get with another guy to make him jealous. Just act civilized and act like it doesnt affect you.When he is finally ready to talk just listen and when he is done depending on what he said(leave me alone for good /Im hurt and i dont know what to do) tell him you are trying to change and that you respect that it will take time for him to forgive you..Dont rush to make out with him,but become friends first when hez not that angry with.Also,all guys like food(well the ones i know)bake him something to show that you are sorry, dont stick around to watch him eat it.You can also write a poem, make a song,if he likes rap do that and it might make him laugh and remember y he liked you in the first place..

those are the worse kind of relationships, always having to reassure the other person that you are trustworthy. i had to reassure a cheating boyfriend that i m not cheating on him. could you believe that!!!!
you have to show him by your conduct/actions. you have to reassure him...and this may not be enough, you might've hurt him too bad. if y'all do stay separated then this will be a lesson in growing up that you will keep forever.