It's tricky because you want to be honest and keep the communication open with your husband--so it doesnt look like "sneaking around" when you talk to your friend, but you dont want your SO to get mad at the same time.
Could it be possible your husband, you and this guy friend of yours all go out on a date for dinner or a drink, something casual and low pressure--your guy friend can bring his SO or girlfriend with or even his daughter? Then your husband would get a feel for how the guy is and how yours and your friends intention in staying in touch is totally innocent.
Or you could prove it, let your husband see in an email that your correspondence is friendly.
He shouldn't try and tell you who you can and cant be friends with.
Put the situation in his shoes--he has a good friend (a guy even) say 'how would you feel if i told you you couldn't talk to john anymore' ...it's the same scenario.
I hope that doesn't sound elementary--I'm no therapist but if i were in your shoes these are things that I would do to prove my case
