I can't forgive him...

It was so long ago, the bad things that happened in our relationship, but I can never get it out of my head and cry about it and I sometimes bring it up when talking to him which has shown that I haven't forgave him for what he did. I know it sometimes takes time for people to accept things that have hurt them, but this stuff happened a little over a year ago and it's still on my mind. He never cheated or tried to btw, it was because of other personal matters... 
I don't know what to do. I'm happy in the relationship, but when I remember those things I just want to cry and I even get mad at him at the thought of those. I know that it is immature of me to do that and I have brought it up with him how I am too immature for a relationship, but he said he was willing to deal with it and work it out, but none of it has been worked out.
He is sweet to me now and of course there are bad moments, but I don't know how to feel. I love him. But I feel like it's going to hurt him in the long run to stay in a relationship where I can never forgive him for things that were even so long ago. 
I realize how I'm in the wrong here for my immaturity, but what do I do? Please help...