Me f19 and my partner m21 haven't been able to see each other for 6 months due to him being in jail. I'm staying no matter how long, he's being overcharged and hasn't seen trial. He didn't do anything awful. Plus just before he was arrested we went through pregnancy loss. He isn't just some boyfriend, he's the most wonderful, kind, empathetic, and exciting person I've ever met. I want to marry him.

The issue came about over a mutual friend (fake name Mike), whom had added my fwb (fake name Abby) to a snapchat story where he posted NSFW pictures. She was scrolling through her stories when BAM, Mike's member on full display. I gave him shit about it, and asked him to remove Abby because she didnt want to be on it. I told him "why aren't I on that story? Hell, I'd already seen it before I met you!". (Me and Mike initially met on the internet before irl, he's a content creator). He then asked if I wanted to be added, I said no but said "I'm hurt I wasn't added to begin with" as a joke, which I assumed registered to him because he laughed. He then added me to the story, but I asked him to remove me before he posted anything else on it.

When I told my partner, he said he didn't like it. He then reminded me of our main boundary in our openness, no friends. I assured him I have no intentions of that nature with Mike, it was meant to be a joke and seemed to be received as one in the moment, but he still felt weird about the whole thing. I understand why, but I'm in a bad situation here. He's in jail, we can only talk for 15 minutes at a time. We don't have the option to have thorough, productive conversations about the situation that will leave him feeling better and reassured.

What could I do/say to ease his mind that I can accomplish over short phone calls? I was considering listing everything I'd be risking by betraying him like that to put it into perspective how ridiculous it would be for me to consider cheating, and then apologizing for what i said, but that seems a little but to centered on me, is that a bad way to frame it?