How to get my fiancées trust back after 17 year lie

Hi, I would like some advice, should I fight for my partner or let him go?
I have been with my partner for just over 20 years, we met when we were 14, had a son just before we were 16. He gave up a lot to be with me, university and of course his freedom of being a young man, he stood by me and I was a horrible person, I hadn't had the best upbringing probably the worst abuse imaginable but I thought I found my Mr Right, he was amazing. We got a house together and things started to go down hill, bills to pay, baby to feed and every day life seemed a bit impossible, we were only 16 and life was tough for both of us with no real support. We would be angry to each other and quite abusive physically. I ended up cheating on him and ended our relationship, for 4 weeks he would try everything to get me back but I was so cold and nasty to him basically wouldn't give him the time of day to the point where he became suicidal ( I did not know this at the time) during the time we were separated I had sex with this other boy, when I eventually told the other boy it was over because I wanted to get my life back and do what was right for my son. He seemed fine as he said he fancied another girl, he ended up raping me and him and a few friends of his laughed and said I was damaged and there was no way my ex would want me back. A few weeks went by and I managed to pull myself together to fight for my ex, I told him I made a mistake and wanted him back, he said no, I told him I was going to move away with my son, he asked if I slept with the guy and I said no I did not. Our sex life according to him now and he is correct was terrible up until the last few years, I always found him sexually attracted but couldn't bring myself to have sex and this was obviously because of what happened to me. Earlier last year we started to plan our wedding and I wanted to tell him at least something about our time apart but I didn't want to say about the rape part. I told him I did sleep with this boy which devastated him as he thought I had only ever slept with him. I then told him about 9 different versions of the story and then when he threatened me with a lie detector I had to write a letter with the whole truth. Now he does not trust me which I don't blame him but he is willing to throw away all these years spend together with 3 beautiful children, good jobs, our house and cars. I deeply regret not telling him sooner, he says he never would have took me back had he known the truth, I've robbed him of 17 years of his life that he will never get back, he could have had a better life. He now wants a trial seperation but has told me there's a very slim chance he will take me back, the trust has gone. He has had a revenge affair after I did this but didn't sleep with them because that would be too far. My life has collapsed, I am a better person that what I was back then. Back then u lied to get him back, when I was chopping and changing my story a few weeks ago j was doing this to save what we already had, he doesn't get this and he thinks I should have never had him in the first place. Should I fight to keep him or is the right thing letting him go to make a choice he didn't get 17 years ago? My heart is broken I've caused so much damage and hate myself for what I have done. Please people give me some advice.