It takes somewhere between 3-5 years to heal from infidelity, and some people never do. It's not something that your marriage can quickly come back from, even if your WS is doing everything right. And if they are refusing to do the work required... forget about it.
It's not something that you can work out on your own, so I would suggest finding a marriage counselor if you haven't already. It's great that he's in individual therapy, but you need to be going together as well. You're trying to heal the marriage, and he only makes up half of it.
He should be doing everything possible to make you feel as safe as possible and to earn back your trust. He may need to put more work into that if you feel like he could still be cheating. To be honest, even if he does everything right you will still have doubts sometimes. I would recommend buying the book How to Help Your Spouse Heal From Your Affair by Linda MacDonald. It is good for both you and your husband to read. Another good book is Not "Just Friends" by Shirley Glass.
It took 23 months for "I forgive her" to come out of my mouth, and everyone who knows about it was shocked that I said it at all. That was 2.5 months ago and I meant it when I said it but between our D-Day anniversary, wedding anniversary, and a triggering situation that came up recently, I wouldn't be able to say it right now - and that's okay. Forgiveness is a process and it doesn't happen overnight. It also doesn't "just happen" though, it took A LOT of work to get there.
I don't think it ever stops hurting entirely, but you learn to move forward with that pain. Personally, at this point, I mostly just feel sad that it's part of our story.