Mostly separate, but in most cases we do know the partner but don’t always socialise together, it’s a total mix.
So:
My school friends - I see individually and in groups, sometimes with partners, sometimes without. Arrangements are all made through me, DH isn’t in contact with any of them separately apart from maybe FB friends.
DH’s uni friends - the same but the other way round. We met a long time post-uni.
Siblings and their partners (both sides), cousins etc - see separately and together.
School gate type friends - the primary friendships are between the women but in a lot of cases the men join us occasionally to go to the pub or if someone has a party, but the women meet either in groups or separately maybe once a fortnight, male partners once or twice a year.
Friends made through work - nearly always completely separate, DH doesn’t tend to keep in touch once he’s left, I still see 4 or 5 people from former jobs
Friends through hobbies locally - mainly separate although sometimes in couples.
I’d say about 90% of my socialising is separate from DH. It’s easier to organise and I don’t like being in his pocket. I can only think of one person I know who won’t socialise without her husband and we all think it’s a bit odd.
edited to say odd as in unusual, not in a negative way