Yes, you’re overreacting.
I can imagine that co-parenting is challenging even in the best of times, especially when you throw new partners in the mix. I know I personally would have a lot of feelings about another woman being involved in my kids’ lives if my husband and I separated. But I hope I would be able to deal with those feelings on my own, for my kids’ sakes.
Maybe the boyfriend was posturing a little bit, but who cares? That says more about him than it does about you. Maybe he’s nervous about the prospect of meeting you. Don’t show that it bothered you. Don’t “accidentally” hang up, don’t talk to your ex – because she’ll tell him everything, don’t start drama.
Your kids should be the most important thing to you, not whether some guy who’s probably intimidated by you is disrespecting you. If you make a big deal about this and harm your co-parenting relationship, that harms your kids. Let it go and focus on what’s important.
Be cool when you meet this guy. You’ll get respect by giving respect.