TLDR; I asked my gf's bf to honor an agreement he and I had made about not texting during "date nights". He got butthurt. AITA, or is he?

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I've been dating S for about 4 months now. In that time we've gotten very close. We spend most nights together, and would live together except for integrating our kids would be ridiculous. We call each other our anchor partner, and intend to spend the rest of our lives together. There is definitely hierarchy there that we have both agreed to.

S is also dating a married couple. Her time with them has been impacted by us dating. She still sees them frequently (overnights every other week for 2 or 3 nights, plus scheduled dates when they find time with work and family obligations), but her communication around texting has changed dramatically with them. They used to all group text constantly, and now when S and I are together we frequently put phones away. I know this doesn't feel good to S's couple.

The husband of the couple and I have agreed that when anyone is on a "date" with S, we'll try and limit communication. We both understand that texting happens, but if you are on a date night, I'll try and give you deliberate space and he should as well. We made this agreement based on some early hurt feelings on both our parts. It seems reasonable.

Earlier this week S and I went into the city for a date to the ballet. It was lovely. We had plans for dinner after, but didn't end up eating downtown based on timing, and instead headed back to the burbs and ate closer to home.

Immediately after the ballet was over, hubby texted in a group chat "Hey! I hope the ballet was awesome!". I ignored it. He also proceeded to text S a few times, but she managed alerts on that. He was pretty hurt that she didn't communicate further with him that evening. Not for me to manage, but I am aware of it.

This morning I sent hubby a note and said "Hey. I get that you were being friendly, but I'd appreciate it if you could respect the boundary around communicating during dates in the future. Your text after the ballet was a bit much". He got pretty angry. Made mention of how much time I get with S. How little time he and his wife get with her. How she sometimes texts me when she's on a date with him. How it's not relevant that I left him and S alone when they were on a date last week. How I had wanted to be more included in the "group" and feel like a part of the polycule.

My question. AITA? Should I have just let sleeping dogs lie? It was only one text (that I had to experience, S had others to deal with). I reached out to him because the boundary breach was between he and I. We had specifically agreed not to intrude on each other's dates. I've been honoring that boundary vigorously, because it matters to me that he does as well. I felt that reaching out now prevents me getting even more frustrated the next time he texts on a date. It was bugging me that he had texted, so I wanted to communicate with him about it.

Or, is he the asshole (IHTA?)? Is he just butthurt that he doesn't get as much time with his girlfriend as he used to, and me reinforcing any kind of boundary is going to hurt his damn feelings?