Trust takes seconds to lose, but potentially years to regain. The best thing to do is to give yourself time. There is no quick and easy way to speed this process along. Just give yourself time to evaluate your feelings. Depending on why your girlfriend lost your trust. You may find it practically impossible to replenish the trust you once had for her. Try talking to her and tell her just how you are feeling and tell her what she can do to make this process easier for both you and her. I hope this advice is helpful for the two of you.
You have to deceide what is most important to you. If you want your relationship to contiunue you have to trust you have to try. But you also need to be honest with her about your trust isues. If she loves you she will want to work with you to build the trust necessary to advance your relationship. If she doesn't then she won't but these are questions you should be asking your girlfriend. Tell her "How can I trust you as a girlfriend?"
You want to tell me I am the worst please do. You want to tell me I should have been better please do. Now I know why I forgot in the first place.
Sometimes it's okay to give someone a chance to rebuild broken bridges, to reinvest in relationships, to repair and heal. Communication is key when it comes to trust that has been compromised. Trust takes time to build, but seconds to lose. However, the good thing is that it can be recovered, put together piece by piece, but it takes time and effort. If you love her, and believe she loves you, then talk to her about your trust issues, and how she can alleviate these issues or not give you a chance to have to worry about her compromising your trust again. Hope this helped.