I am glad, Mummee, that you feel your relationship is worth what you went through. I just wonder whether you feel it is worth the 'shit' as you put it, that your relationship has put your OHs family, particularly his DD, through?
Because whether you like it or not, you only have his word about what happened during his marriage and if it was so bad, I just wonder why he stayed as long as he did.
FWIW, my parents separated when I was about 11 and even after all these years, I still find it hard to deal with, because whatever you say, as a child, it does feel like its you who is the cause of your parents break up and it does hurt to lose your dad. Even though My dad and I managed to continue to have a good relationship right up to when he died, I can't help the fact that I d8 resent the things my half-sibling had that I didn't. Not material things, but time. I saw my dad a few times a a year. It wasn't my dad who came to see school productions> My dad wasn't there the day I opened my o level results. He wasn't there to share the 'dad/daughter' moments that so many of my friends had with their fathers. he wasn't even there to shout at me when I stayed out beyond curfew time. I never went on holiday with my Dad, never, after the age of 11, woke up with him their on Christmas morning. So many things and times when a daughter wants her dad there and he wasn't. so yes, I do resent my half -sibling because they had all those moments in their life. I don't blame them, it wasn't their doing, but I do resent the fact that what they regard as normal, I never had the chance to have.
Don't lay all the blame for how your OPs DD feels about him at his EXWs door. Like it or not, your partner bears at least half the blame because he did leave his family, including his DD, to be with another woman. It doesn't matter how long you waited to 'get together', the fact that you were on the scene before he left is probably enough in her mind to regard you as at least part of the cause for his leaving.