Just seen your thread OP.
You say you had it confirmed by your H that he was "seeing someone else" and had a secret relationship with another woman for what sounds like 18 months - and yet he won't agree it was an affair?
Sorry, he is being extremely manipulative here and worse still, is putting the blame on to your jealousy - and now, your perfectly understandable mistrust.
Emotional infidelity is characterised by three things. Secrecy, physical chemistry and when the friend knew more about your marriage than you knew about their friendship. All 3 boxes are well and truly ticked in your case. If your H needs convincing that he had an affair, get him to read Not Just Friends, where the above definition comes from. Moreover, it might interest your H to know that his actions are grounds for divorce, since secret "friendships" are held to be unreasonable behaviour. I'm telling you all this so that you don't start to question yourself about your perfectly reasonable disquiet and mistrust.
It doesn't surprise me that while this affair was going on, your H said that he wasn't sure if he wanted to work on your marriage, but I am puzzled about why you accepted this and it took from this conversation in the autumn until February to discover that an OW was indeed involved?
Also, if your H is trying to claim the autumn conversation that you initiated about the problems in your marriage, as evidence that he had tried to resolve things, this is also disingenuous and highly manipulative. These conversations happen a lot during affairs, but they count for absolutely nothing because the biggest obstacle to the marriage getting better and recovering is being kept secret.
You won't get past this until your H stops minimising what he has done and stops trying to manipulate you. A third party like a counsellor would have no trouble seeing this as an affair and sometimes (like on here) just having someone else telling it how it is can force someone out of their denial and stop you feeling like you are going mad.
I am not ignoring the marriage problems you say you had before all this, but having a secret affair is just about the worst remedy for marital discord and is in fact the most passive-aggressive way of expressing dissatisfaction. Your H chose to do that and he needs to take responsibility for that choice. All the time he was in a relationship with this woman, he was sabotaging your marriage but you didn't know it.
In effect, he is still sabotaging your marriage, but in a very manipulative way so that he is trying to paint this as your fault for being jealous, unreasonable and mistrusting.
In terms of communication, stop texting eachother and consider counselling to get through this. While you're waiting for that, read Not Just Friends together, because you really aren't on the same page about what happened here.