20 years...and falling apart!

Not sure where to start , however I do know I need some advise desperately! I have been married for 20 years to my one and Only! We've had our ups and downs, like most couples but everything has finally come to a head and I am so lost and confused . To keep this as brief as I can......we married young,me (18), Him (19) I always knew I wanted to be married but he did not thru our younger years and this resulted in a confession to me after 10 years married. He cheated on me three times.
By this time we already had our first son. I decided to give him the chance and he has proven himself time and again for the past ten years. It was me who didn't take the chance and I had a terrible time trying to deal with forgiving him completely.

I would live in the past and every given moment I would through it in his face about what he had done. Why? I have muttled thru my feelings, hate, resentment, Depression and finally sickness , this all happened because it was like we never even skipped a beat and carried on with life going to work, raising the kids...etc.. I needed constant reassurance and I became sooo insecure because of this and became so blind to how good he was to me. He always said he would make it up for the rest of our lives and he has. So trust was my biggest issue with him and it led us down a cold and unfeeling place where there were no more friends, practicly no family , and no happiness because we were suffocating eachother and both of us were officially doing it to ourselves and eachother !

Now that it has come to a head we both agree that we want us to stop hurting one another . I have never seen it more clearly than ever before, but is it too late?
He has become very distant and is very depressed, says he doesn't know if he can give me another chance because he doesn't think I will "let him live it down" or forgive him completely. Now that I know that he is sincere and has been and I actually see it , I know I can get past it. But now it is him who has the change of heart and I just don't know how to tell him that I do forgive him and want him, and love him and trust him...it just seems like the rolls reversed and now he won't come around to trusting me or beleive me. Neither of our doings make this right....We have a lot of work to do , I am fully aware of that and we will be going to therapy but will it be enough?