It's a shame you could not stick to the plan. Validation by the family is not nearly as important as CL feeling safe and avoiding as many triggers as possible.
Yes, he did say that you should go, after all. But he was backed into a corner.
Perhaps it would be best for you to take the reins, and tell him you want to stick to the original plan---then stick to your guns with his family.
At this point, I think it's time---perhaps after the wedding--to quietly let your families know the truth of what is going on. Not necessarily in great detail, but with enough honesty that CL will not again find himself cornered in this way.
I have two sisters who are BSs, and I am, too. My mother is no longer alive, and I am estranged from my personality-disordered father, so neither learned of my husband's infidelity or our separation. They did, however, learn of my BIL's infidelities. They were VERY supportive of my sisters and BILs. One immediately wanted to R, and they could not have possibly received more support from the family. (I was a young teen, and babysat for my nephew when they went to MC, even.) The other was not sure about R; her husband more blatantly cheated, left for OW, etc. My parents were financially supportive when he bailed (including providing an attorney's retainer), but---here's the thing: they were also COMPLETELY supportive when my sister chose to R.
When my husband cheated, I didn't tell anyone until separation was imminent. My sisters were SO sad I hadn't told them. (I didn't want to trigger them.) They really wished they had known to offer support. When a reconciliation attempt (after separation, when he "came home") failed VERY rapidly, they were also very supportive.
Really, they all just wanted me to be happy.
I think it's probably reasonable to believe that CL's family and yours would want YOU to be happy, as well.
If you were to tell them, then the pressure to attend festivities with which you are not comfortable would ease.
I know it's late to let people know, in light of the imminent nuptials; you don't want to cast a pall on them.
But after the wedding, it's time to be authentic. Don't you think? In this revelation, I would be sure to let your families know that when you opt out of activities, it is because you and CL have carefully made the decision together---and that they don't need to find solutions for you.
I don't know how to help CL at this point. He was so guilt-ridden about feeling BETTER with the prospect of your absence at the wedding. He was very conflicted---but ultimately knew he could not handle it, emotionally, otherwise. And now you are going.
I guess I would give the advice I'd give anyone: be sensitive to triggers. Step outside yourself and think of your BS. Anticipate problems before they occur and, whenever possible, steer yourselves away from them.