Should I be worried about my husband chatting his ex at 2am?

So I woke up last night to get water and my husband left his phone on the couch. I saw a notification — it was his ex. They were texting back and forth at 2am. He claims nothing’s going on, just friends catching up. But they dated for like 6 years and he never even came out to our families until after they broke up. Now they’re “just friends”? Feels off. I’m bi, came out later in life, and we’ve been married 3 years. I thought we were solid. But he gets weird every time I mention her. Changes the subject. Last week I asked if he still has feelings and he said no, but it felt like he was saying it to convince himself. They both live in the same city now, went to the same queer book club last month. He didnt tell me until I found the event in his calendar. When I asked he said it was no big deal, just community stuff. I dont even know what I’m asking. Just — does this feel like a red flag or am I being paranoid? That silence when I bring her up. He never texts anyone else that late.