I think you are focusing on the wrong thing. I get that OW isnt someone you care to be friends with or really even meet. But SHE is not the problem. She is a symptom of the problem. If it werent her, it would just be someone else. Worrying about their relationship is only going to bring you down.
What Id be more worried about is him disappearing for months and then expecting you to just let him take his kids for a few days. What kind of schedule is THAT? Why are you just letting him waltz in and dictate when to take your kids this weekend? Id say that you need to agree on a custody schedule before just letting him take them whenever its convenient or fun for him.
