My broyfriend went with prostitutes in germany 11 years ago, do I forgive him? i'm so gutted & he feels dirty?

My boyfriend went to work in Germany 13 years ago for 18 months on and off because there was no work for brickies over in England. We had an 2 year old little boy with special needs and he ured me it would be all work and no play and he would send money home for the family. He'd been there several months and become distant, didn't call when he said he would and refused to come home when our little boy's needs became more significant. I was struggling to cope but when he finally did come home, he left us and moved into a flat. We carried on seeing each other but he woulodn't re-commit to us. I saw a couple of lads and he said he didnt want a relationship with anyone. We eventually got back together (his lease on his flat ran out) and he moved in, we got a mortgage, had another little boy and started to build our dream house. Everythings been great for the last 8 years (I occasionally find out he's lied aobut something or other), however after talking to one of the builders on our house, putting two and two together, and bluffing him, I found out just before new year that whilst he was in germany he was using s (6 or 7 times), smoking pot and drinking heavily. He's full of remorse, crying saying he doesnt want to split up but I just cant get my head round it. Our house is nearly built, our children love him (he's a good dad) our eldest is disabled and depends on his dad a lot, but i just can't stop crying. I'm normally such a strong person, but feel I cant discuss it with friends because of the shame of it. I am intelligent enough to know that what he's done is to do with his character, and even though I know he genuinely is remoreseful (he's said he felt suicidal whilst crying on sunday) i don't know what to do. It hurts so much. My dilemma is that he's been such an ******** in the early days, but is very good now. Any advice would be appreciated. Thanks.