My heart really goes out to you.
If there's still love, both ways, between you and your husband, perhaps he would be willing to consider counselling to find out what has changed to cause him to feel uncomfortable in a sexual relationship with you?
If he's not willing to mend your relationship together, I don't feel that polyamory is the solution. Polyamory is never the solution to any problem between couples, it usually only makes existing problems worse. Polyamory can put a strain on the most solid, functional relationships, and asking you to watch him go out with other women while you're not having your own needs met, that's unfair to you. You deserve to treat yourself better than that!
Gralson = my husband
Auto = my girlfriend