You've had some brilliant advice here OP.
I'll just add my experience to the mix in the hope it might help a nit.
Ex had an affair for two years pre-break up. I 'knew' in my gut but couldn't get proof, he denied till he was blue in the face. When I finally couldn't take any more, I threw him out. Twenty years married, three teenagers. He walked away, moved in quickly with OW, dusted himself down and started a new life. Just one little sentence to describe what he did. I could write a book describing the fallout for me and the kids, and I still wouldn't cover it all. I was devastated, it was like the four of us had been thrown under an emotional bus.
Priority was the kids, their wellbeing was my priority. Two took it quite badly. That first summer was spent ferrying them to counselling, wiping up tears and trying to put a brave front on it all. His first summer post break up was spent sailing around the Med.
I quickly filed for divorce, knowing it was over, and assuming because he was now living it up in his love nest with OW, it would be straightforward. How very wrong was I. He ignored letters, he stalled on every aspect of the process. What should have taken six months took twenty. I was baffled. Why do this? Because he couldn't deal with me taking control.
"This is moving too fast" and "I will decide if and when we divorce" became his stock response to my solicitor. He deliberately made a difficult process far more complex, expensive and lengthy than necessary. Why? Well, because he could for one thing but also because he was angry with me, bloody furious. He would come round to see his kids, in between many holidays, weekends away with his OW (now his open partner), concerts, etc., and the anger towards me radiated off him in waves. Why? Because I hadn't crumbled, I was coping, after the first couple of months I was actually doing well. His ego couldn't cope with how I could function without him. So he punished me by stalling on the divorce. Mad, irrational, but that's how he operated.
So, five years later and I have very little contact with him. I hardly think about him. He is still with his partner, but apparently the cracks are showing. Because he invested so much in their relationship, he's determined to stick it out, after all he gambled us, his home, his extended family on a fairy tale future with her. She has become needy, insecure, quiet and withdrawn. His laid back carefree facade has slipped to reveal the passive aggressive control freak that has always lurked beneath. Neither trusts the other, they both had an affair, what is there to trust.
Yet, in the early days OP, I felt jealous. But looking back it wasn't jealousy really; it was resentment at the unfairness of it all. I knew she was having the best of him, and my early years with the best of him were the happiest ever, whilst I was dealing with the worst of him. Also I was floored by the sheer enormity of being a single parent, a sole adult in the family home, whilst he just seemed to rewind to his late teens, with a clean slate.
I've rambled, I'm sorry. Just take this if anything: don't think about how far you have to go, think about how far you've traveled. You are doing very well. You will get your divorce and you will be happy. You're stronger than you think. And don't think for one minute he'll be the one with the happy ever after here; his behaviour already proves otherwise.
I wish you well x