DP and I are due to get married in the summer, we have a 3 month old baby boy. DP hasn't confirmed a best man yet, no brothers, no male cousins he's close to. He has 4 main groups of friends, the partners of my friends, some colleagues, 2 guys he did his undergrad with and then one girl he did his masters with, she's 4 years younger than him, they have only known each other for 3/4 years. He meets up with her on his lunch break maybe once a month as they work near each other, then they maybe go out for dinner/to an event once every 6 months. I've met her, she's nice enough but I think I've met her maybe 6 times in 3.5 years, she hasn't met DS but did give a gift/card. Notably when he was doing his masters it was a group of 4 girls and 2 guys, one of the guys has moved abroad, he doesn't talk to the other 3 girls, even though his friend is still close with them.
DP has said he wants her as his "best man". He claims he doesn't feel close enough to anyone else right now and thinks she would be good.
My issue is this friendship has caused issues in the past, she's incredibly attractive, and tbh I've never really been certain on men and women being super close friends (fine as part of a wider group). When he was doing his masters I did feel a bit weird about her, they used to message all the time though that faded when they graduated.
He has friends he sees much more of, but claims he doesn't feel as close to them.
AIBU to feel uncomfortable with his choice?