would you be happy if your partner had a best friend of the opposite sex?Watch
Ideally I’d make them my friend too and team up with them to do nice things for my partner
People can have platonic relationships with the opposite sex but I wouldn't be relaxed or happy if they were his best friend.
If you cant even handle your partner having friends, you shouldnt be in a relationship.
I naturally get more along with girls than guys and although I will admit in the past I have had feelings for one of those friends, the vast majority I don't and we have in fact mutually 'freindzoned' each other. As long as boundaries are clear in a relationship/friendship then there is literally no problem with both sexes becoming friends. If anything it's extremely healthy to get someone's view point outside of the 'bubble of masculinity'.
It's all about trust at the end of the day if they just say they are a friend then believe them or not, but not believing them indicates something wrong with the relationship and perhaps you two aren't meant to be together.