Providing emotional support and having a full relationship with someone are two different things. I think your relationship with that man is very limited in what can happen and what will ever happen, assuming you don't leave your husband.

I think you're idealizing this man because you don't have to deal with all of the ups and downs of a relationship like you have with your husband.

It's in your hands to continue the relationship or stop the relationship. You need to be fair to your husband who probably has supported you through a lot over the years - you shouldn't string him along while going elsewhere for emotional support.