Infidelity Support Group
Any relationship in which one partner engages willfully in sexual relations with another outside of the partnership is considered to have experienced infidelity. This breach of trust is often traumatizing for the faithful partner as well as the relationship, and support is often needed to heal emotionally and to decide whether or not the relationship should continue after...
Hang in there.
You said it yourself, you spent so much time focussed on his recovery that you got shortchanged. Are you in an counselling? You may benefit from it.
I wish I could answer your question about being able to trust. I am struggling with that as well. My counsellor suggested I start interacting socially with new people through volunteer work and group interests, not in an effort to meet someone new (I'm still married) but to start to interact with new people. If I can start to trust others as friends then maybe one day I'll trust someone with my heart.
I really don't think casual sex will help that. If anything, it will allow you to not trust even more.