I've also been struggling with a dwindling sexual dynamic with my husband, alongside a very exciting one with my bf. Before having a bf I thought I was just sexually broken, no libido. Now I realize it's far from the case. Having another person to remind me that I am a sexual being, and make me feel good about myself sexually, has been great. It also helps me see the differences between what works and what isn't working. I've been giving my husband more specific feedback about things we can change in the way that relate that will increase my interest in sex with him. Whereas I used to just forget about sex.
One thing that makes it work better for my husband is that I don't have oral or PIV sex with my bf. Sometimes that's mighty frustrating, but we get creative and have good times, while my husband feels like he still has that important part of me to himself. It's enough for me to feel like I'm keeping my sexuality tuned up. Could the two of you reserve something that you only do together? It could even be tongue kissing.
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