<human>: Can you succinctly summarize the text in 1-3 sentences?

Hi, I've recently started dating my boyfriend. We'd been dating for maybe 3 months and made it official a month ago. From the beginning he told me he's still best friends with his ex because that's what they were before dating. He explained to me why he broke up with her and so on. It didn't bother me cause to me it seems he genuinely has no feelings towards her anymore other than friendly ones. 

When the relationship began I kind of expected him to tell her he was with me officially now since, y'know, that's what best friends do. But for some reason he didn't. He mentioned he's very private about those things and I guess I brushed it off. Recently I found her Instagram account (I didn't stalk her to find it, I stumbled upon it through a mutual friend of hers and I) and I found a picture of some quote saying something along the lines of "No matter who you're with and how much it hurts me I will still love you." And she tagged "i still love you" and "best friend" among other tags. That's when it started to make me uncomfortable that they'd hang out for long periods of time and that they're constantly texting back and forth. I just need advice on how to bring it up to where it won't be this huge confrontation or I won't be seen as the over reactive jealous insecure girlfriend. Any tips? 

(I've never met her and don't want to until this is resolved and we can all be on good terms about this. Also don't want it come down to him having to pick between us...)
<bot>: bf's ex/best friend is still in love with him and idk how to bring it up to him without seeming jealous and insecure.