I think I'm the person he's closest to (period) and same vice versa. This wasn't always the case, but has come after years of our friendship/relationship evolving. Back in the early years he would have said one of his other friends and I too.
We both have our own great, long term close friendships with others which cannot be substituted, or replaced. Feeling closest to your husband doesn't = you don't feel close to and value your same sex (or whatever) friends too
Personally, what I like to avoid is the type of man who shuts his own life down as soon as he gets into something. Stops talking to his friends, stops going to the gym, stops doing his own hobbies. That would freak me out. Its important to me that DH has his own friends, has his lil man catch ups and a solo hobby or two.
I'm not crazy on men who say their Mom is their best friend, but apart from that I'm cool lol.