For me the D-day was almost 5 years ago and we seperated at the end of February. He could have gone back to his parents but they lived 100 km away and he had a work here. Actually the company was having troubles and he wasn't getting paid for months so I didn't have a heart to make him leave.
We were living together after we broke off and he was in a relationship with OW. I wanted to get back at her so we still had sex sometimes. I even helped him to choose a hotel when they were meeting, he couldn't bring her to my home and she lived far away. Somehow he had money for that 
I was thinking that she won the battle, but I would like to win the war. That was stupid of me of course. It's easy when people are saying don't do 'pick me dance', but it's much harder when you are in this situation. Lesson learnt, wouldn't do that again!
Since she was leaving the country for the summer, we somehow got back together and we are still mulling around to this day. Actually he got off pretty easy. But his still OH, we're not married. I bought a flat that's only in my name because I don't want to feel that I have to be with him because of finances (renting here costs a fortune, but I can manage mortage on my own). I have kept my/our day to day bills low so I know that if the relationship broke down I can still survive on my own.
We still don't have kids. I'm becoming 30 next year and it's about time but I'm still not sure about him. There have been few times when I admitted that we shouldn't gone back together, at least to myself and to my closest friends. The heartache easened by mid April and I even had a little fling while I was single.
I can see that in some ways we are fundamentally unsuitable. And it's not only because of him, I have a part in this too. For him it's the sex and for me it's the lack of emotional support. He drinks a little too much to my liking and I do 90% of domestic work. We have our good days and sometimes we have a laugh and fool around, but we're not a team. I have decided I'll give it a year or two and when I still feel the same, I have to find my big girl pants and stop the show. I think I'm pretty good example of sunken cost fallacy.
If it is an OW, try to be smarter than me. And I know how easy it is to write it on a public forum and how hard it is to actually act on it! Still, keep your cards close to your chest if you find anything. I snooped a LOT and didn't feel bad about it. It's not like he would have come clean, he didn't have my best intrests in his heart. He even made long term plans while he had an affair, I don't know how long he would have kept going if I didn't found out. And you also have your DC to consider. If he is cheating he isn't your friend anymore, you can't count on him. But do know that you'll always have your friends, family and MN on your side. Feel free to PM me if your not ready to tell anybody in RL.