We all love our spouses. But love, alone, isn't enough to overcome betrayal. You mention he's a good partner now, but you don't advise what he did to be a safe partner. If he simply switched back to doing the stuff he did previously, without digging into why and how he gave himself the permission to betray the person he purportedly loved, it's no wonder you don't feel safe.
I'm worried that perhaps a lot of this has been rugswept rather than fully processed and dealt with. Healing from this is a two-way street. What have YOU done in order to heal? I know that once you have kids, they tend to become the #1 priority and your own needs and issues become secondary but these types of things tend to fester. Focusing on yourself and YOUR healing is also imperative. TO this end:
Her pictures keep popping up on my social media
Do yourself a favour and block her on everything. I know it can be hard, because you probably feel the need to keep tabs on her and are probably morbidly interested in her life, but I promise you, speaking from experience, that you will have fewer triggers if you do.
Part of me thinks I should go get revenge so he knows how it feels but I couldn’t bring myself to do it then that hurts even more cos he was quite happy to do it regardless of me and my feelings.
This comment suggests to me that you do not believe he fully grasps the enormity of what he did and he does not empathize with the pain you have, and continue to experience. This certainly occurred to me too in the depths of my pain. I concluded that a) it wouldn't make me feel better; b) it would probably make me feel worse (one of the ways I compared myself to OW in the early days was to remind myself that while she was X, Y, and Z, at least I could feel confident about my ethics, and that counted for something; and c) it would be like dropping a bomb on our reconciliation.
I think he thinks I should’ve just moved on by now because he is like a different person but he’s not a different person it was still him that did all these horrible things to me.
Has he said this? If so, this is a major red flag. But if he hasn't, what makes you feel this way? It worries me that you are not communicating about it with him. In the first 2 years or so post-D-day my H and I spoke about the A on a near daily basis. If you're having these thoughts and feelings and ideas you should be talking through them with him. If things are not addressed, they will fester. You're also depriving him of an opportunity to comfort you, which is something that can actually bring the two of you closer together. It may feel counterintuitive but for me, talking about it MORE not less, was a better way to heal.
It take 2-5 years to heal from infidelity. You're still IN IT right now. I don't think forgivenss needs to be the goal. When I set out to reconcile with my husband I didn't set out with the intention to ever FORGIVE my husband for his A. To me it was unforgiveable, and what I needed to do was figure out whether I could live with it and whether he could be a good and worthy partner. What was more important to me was that a) he (and I) figure out WHY it happened; and b) that it never happen again. Somewhere along the way, in that, I realized I had forgiven him.