Feeling stupid and insecure. Am I overreacting?

My partner and I have been together for over 3 years and I’m 5 months pregnant.

For the most part, our relationship is good.

I came to the relationship with a few issues stemming from an ex - he had a female colleague who would message him at 11 at night on facebook because she was struggling with some work tasks and needed “help”. There was also an occasion where I was cooking dinner in the kitchen, for his parents, and he was in bed FaceTiming her. Or the time he stayed back because his office was having Friday night drinks (normally wrapped up around 6-7. 8 at a stretch) and he somehow got locked in the office at a school with this girl at midnight. Because “everyone thought they’d left”. Even after he left that workplace, he would regularly meet her for lunch and I’d be told of the fact after. He also withheld sex and affection from me for a long time, because he told me he was punishing me for getting angry at him for these behaviours.

So anyway that’s in the past but I still have insecurities.

My current partner is wonderful, mostly.

He has a female friend from 10-15 years ago? Idk? But I’ve never met her. Early on in our relationship, she would message my partner after 10pm repeatedly, most nights, and that didn’t sit well with me and I let him know that.

Also early on in our relationship, he made an offhand comment that a lot of his previous relationships didn’t last longer than 3 months because of one of his female friends.

It was never mentioned again and I didn’t mention it again because it had only been a few weeks into us knowing each other.

Now 3 years later, I’ve never met her. He claims he can’t organise anything because I get angry whenever she gets brought up, but he’s never mentioned her, I do when I see that he’s been messaging her behind my back again. Normally he’ll say “I was talking to x and they said y” kinda thing.

I don’t care who he talks to i just wish he wasn’t so secretive about it and if she’s so fucking important in his life, why do I feel like I’m being hidden?