Well “ maybe “ he just didn’t think about telling you. Being depressed can cause forgetfulness but....
Why don’t you offer that all 3 of you go out to lunch that you’d like to meet a friend of his from his early childhood through out school. If he immediately finds reasons not too then something could be going on.
If you do get together you could easily pick up that something is amiss or realize there’s nothing to worry about.
My husband has numerous female friends and I don’t worry about it at all.
Same as I have male friends and he’s not bothered at all.
Is your husband being treated for depression ??