Questions: Family & Friends

Let me elaborate a little. Now, I know of course you want your SO and your friends to get along, and hanging out altogether shouldn't be an issue. But I've PERSONALLY always been of the mind that you just don't hang out with your friends SO's privately or talk to them privately. It feels like a line that shouldn't be crossed to me.
Well I have a close friend who views this a little differentially. She sees no issue with it if we all trust one another. We both recently met guys and have started seeing them, however both of us were friends with each guy before we really started "seeing" them if you will. We met her current SO first, nice guy, and again, we were all friends before they started getting serious. Even before they officially announced anything, I could TELL it seemed to be getting serious so I backed off and do not and have not spoken with him privately outside of what's said in front of said friend or in a group chat that she is in.

Now fast forward to meeting my SO. Again, we met mine at the same time and were friends with him before anything started. From the start he was definitely kinda seeking me out, talking to me more than her and what not so it wasn't really a surprise when we started seeing one another however, unlike the boundary I have myself not to cross... she doesn't really seem to have issue with trying to seek him out alone to hang out with or talk to privately. To my understanding my SO is not really receptive to it. Doesn't hang out with her when she offers, and it's hit or miss if he even responds to her when she tries to message him. Not that I've pressed for details, but they've both vaguely mentioned it here or there.

I don't want to be "controlling" or "toxic" or seem like I'm trying to commander their friendships, but I just am unsure if I'm the one with the issue or if there really is something weird about this.