Sounds to me like you have unmet needs, and either your husband isn't interested in meeting them (maybe because he isn't feeling the love from you either?) or he doesn't know how. I've just gone through a few months of something similar, and what changed everything for us was reading "The Five Love Languages" by Gary Chapman. Now we both understand how to make each other happy, and we have the flirtatious kind of love for each other that we did in the beginning, and then some. (And also, he's secure enough in my love now that my other relationships are ok with him.) Try treating him like you did when he was the new man in your life!
Married to a monogamous man 15 yrs, mother of 2, dating C 3 yrs, and in a romantic friendship with L more than 20 yrs