Jones, I understand that reading threads can be become an unhealthy addiction. Look into older ones like whenwillifeelnormal for evidence of when it works out, and also books like I Love You But I Don't Trust You take a more positive approach to making the decisions you are going to have to make every day.
it sounds like you are aware that he is saying and feeling the sort of things that make it possible to work at it. The lack of trust you feel is necessary to protect yourself and totally understandable, not a barrier to returning to 'normality'. It is a long, difficult journey and one that he's set you on, so don't beat yourself up. Just be aware your gut is a really really good guide on these things, listen to it more than old threads.
Now that you understand what the 'I don't think I love you' was about, the fact that he had said he loved someone else and so couldn't hold in his head the idea that he loved two people, there are many ways to react to this. Pushing forward with what you say above, the emotional conclusions to wrestle with are that either 1. he fell out of love with you and in love with her. Therefore how could it really be over? 2. He thought he was in love with her but wasn't really, in which case, how could he be so wrong, how fragile is his supposed love for you that he can deny it or get confused like that? or 3. He was saying it to test things or leave you or get you to leave him or some other manipulative way to get out of the situation which was becoming intolerable to him. In which case, how cold and hurtful and cowardly.
Because all of these realities cause emotional pain, it's a very difficult thing for you to forget. There's no doubt that it's possible to think oneself in love with someone due to novelty, attraction, passion that is false and a bubble. And it's possible to think because of this that you 'must' not love your partner at home. There is a positive spin on that which is that those people are naturally monogamous in some way, that they would prefer just to be with and 'love' one person, and they freak out when it gets more complicated so have to rationalize. It's possible that you DH is like that and now, through the understanding and reality of his potential loss, has realized his truer, deeper love for you.
That is why people keep going on about the separation thing I think. It's not to chide you I think, but because it is this realization of TRUE loss, that can quite often clear the back and forth fog from a cheater's mind and make it very clear what they really want and will commit to fully. If your DH knows, as we do, that what you really want is to make it work, he has a lot to work with, but also a lot to take for granted too.
Sounds like you're doing really well and I hope you continue to get RL support. Don't be afraid of demanding what you need to keep going. Lots of hugs.