Tell him this "I will leave u if u keep acting like this. I wouldn't mind if u had a girl best friend." Also have babies with him, that will make him feel less possessive since u have a baby to care for
You should assure your husband that there is nothing going on with the both of you. Ask him if you could invite your friend over so that they may get to know each other and be familiar with each other, so that he may get rid of any insecurity that he's having.
it's your husband so maybe he has a right to be jealous. If it was a boyfriend or something, but your married. Talk to him about it and maybe set up some ground rules that he would be comfortable with like only visiting your male friend when he is there too. Marriage is all about compromise, you need to work out something that you both can live with.
I would have him meet your guy friend or invite him to hang out with you guys so he can feel more comfortable with it but honestly you should tell him to trust you you guys have been married for how long remind him that and tell him i wouldn't hurt the man i married and made a vow to love forever that may work but honestly he really needs to get over it you will have friends just like he will have friends you guys are married trust should of already been gain in his part so he needs to trust you or get over it just saying hun.