Good for you, Brook. I find that separating as much financial connections or legal things as possible makes me feel better. It will soon be to the point that the only connection we have is the kids. Mine are older though. Even though we agreed to communicate about kids, he consistently contacted them about getting together. It backfired. The kids kept turning him down, whereas I would have just said, OK, you are going with dad today. Well his loss! He has not seen them all summer. I have had a good time with the kids and have done things we wouldn't have, otherwise.
I am glad you are enjoying the time with the girls. They are only little once. You can never get those times back... and they go so quickly. Mexico will always be there...
Don't let his decisions get to you. And it looks like you aren't- good for you. It would be easy to let these things get the best of us. But you are enjoying your time with the kids, you know what is important, and you know to cut off the legal/financial things to support yourself, but detach yourself. You are a great role model for the boards!