Oh gosh I do know just how you feel. Our BS's seem very similar in their pain. I had a melt down myself a couple of days ago.
I wish I could say it gets better quickly but the truth is it has happened very, very slowly. Much of it has depended on me fixing myself so that I can actually empathize with him enough to really understand the depth of the damage. That process takes time and so being able to give him what he needs to heal does too. The result is that we are on very different places on the healing curve.
The bright side, if there is one to all of this, is that I am finally having the courage to figure my shit out. Issues I thought I would never ever acknowledge or discuss are getting out in the open now. First to me and my therapist, then to BS and our MC, and finally, if it's appropriate, to my family and the world at large. It's a transition from hiding things in darkness with fear of exposure to being willing to step into the light.
Like all transitions, things usually don't go smoothly. In the past I formed and maintained relationships with people based on the way I felt in their presence rather than on the way they and I actually were. I'm working on changing that but in the mean time I'm in a relationship NOW with someone who is in agony much of the time. It does not feel good to be in his presence when he's showing his pain outwardly. My impulse, my old and crappy coping mechanism, would be to distance myself emotionally and/or physically. The challenge now is to maintain my equilibrium while having this really uncomfortable experience of witnessing his pain. It takes a lot of mental energy to override that impulse and I think that's why we get tired.
You know by this time that there's no magic bullet. Infidelity creates terrible, life changing wounds. When I was 18 I was hit by a car doing about 40 mph. Miraculously I did not die but the injuries I sustained have had life long effects on how some of my bones and joints function now. It's something I wish didn't happen, and I'm really glad I survived it but I will never be the same as I would have if it didn't happen. I think it's about getting to acceptance.
Okay this got very rambley and I have no idea if it's helpful but in any case I wanted you to know that I can relate to your feelings and they are perfectly natural feelings to have given our situations.
Strength to you, sister, from a fellow EvolvingSoul.