I find it quite common that a man in a relationship has no friends. This has a really unhealthy effect on their relationships with their partner. I see it happen to friends and suffered it myself with my friendless ex.
I had all kinds of crap as a result
- guilt trips if you dare to have fun without them
- having to decline invitations cos you worry you are seeing your friends too much
- sometimes inviting them along with you, but they make zero effort to integrate and you feel like a mediator trying to get them involved
- feeling responsible for their happiness, suggesting clubs and hobbies in the hope they'll change (but they wont)
Anyway it's a huge red flag for me now, I'd warn any of my friends to stay clear from such people.