Yes, I lean towards not going to Mexice - though of course it's up to you. My problem with is is - why play 'happy partners' (ie: going on a trip together) while he is conducting a R outside of your M. I would certainly rock the boat on that one - and organise a nice trip for myself elsewhere. He can explain that to his friends.
As for OW's H. That's a tough one. I didn't know the guy in my sitch and he was abroad. However, the dynamic was similar. H told me OW was unhappy with the guy and he was controlling and a bit crazy. However, she had recently moved continents to join him, so was he really that bad?? There was a definite 'rescuing' theme there too.
I tend towards taking the higher road. OW is beneath your notice. She is your H's problem. That is his life, not yours. And while he is in a R with her, there will be no R with you. That's the road I have taken and I haven't regretted not engaging with OW at all. I did know her a little as she worked with H and had met me at a function before the A began.
Anyway, hope all of this helps a little and good luck xx
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus