These are my feelings on the matter:
For me personally, trust is something I have to make a conscious decision to do. For quite a while I believed that if I want to stay married to fWH I would have to simply accept that I will never trust him again and I'd have to live with that - it didn't work for me, I was obsessing all the time, it was making me angry and it hurt...
A little while ago I realised that if I am going to commit to this marriage and be HAPPY I have to be "all in" and that involves trusting fWH. I looked long and hard at his actions and they led me to believe that it was okay for me to give him my trust. But it's not a one-off thing, I literally have to decide to trust him daily (and sometimes doubts creep in and I have to shove them away and occasionally I have "wobblies" but I work at recovering from them). For now I feel that I am happy to trust fWH, provided he is showing me that he is committed to me, that he is working hard to be the husband I deserve. The moment he starts behaving like a jerk, I withdraw the trust.
This is working really well for us. I've only been at it for a little while, but I have felt calmer, happier and more optimistic about us than I have since D-Day. I am hoping that as time goes by this process feels more natural and becomes our "new normal" but I will ALWAYS have that disclaimer...the moment he returns to wayward thinking/behaviours the trust is gone!