<human>: Give me a shortened version of the text

Started seeing someone I met online in August. We'd been hanging out for about a month or so before things got romantic. We recently had the conversation that we were exclusive. We've already talked about our past relationships. He has one ex in particular that he's still friends with. I've felt a little insecure about it because he always talks fondly of her (they live in different states now), but mentioned that he 'thinks they're better just being friends'. hm. note level of confidence on that one... but I try not to be paranoid bc I'm 28, he's 33... anyone I date now is going to have past relationships and I understand being friends with your ex is something adults do. Just browsing instagram and see he posts a #tbt (where people on instagram post an old picture as part of "throwback Thursday") with his ex girlfriend and one of their friends... who isn't tagged. BTW he comments on everything his ex posts and vice versa. and I'm a little annoyed. I fall asleep for a bit and wake back up and notice he has taken it down. Anyone else see this as a red flag or am I being overly paranoid? How do I bring up the topic to him without feeling like a 15 yo especially now that he's deleted it? I just happened to see it the one second I logged on.

cross post from /r/dating_advice
<bot>: Me [28 F] with my SO [33 M] new relationship, posts #tbt with ex gf literally days after we become an item. how annoyed should I be?