Having conflicting feelings in my long term relationship

I have been with the same guy since I was 17 years old, so six years. We own a house together and we have a dog. Lately I’ve been having issues with my depression and it’s just simply taking over which is causing me to be distant.

Recently he had a breakdown and told me he is also feeling “sad all the time” because he has had a rough year (he has). When he told me this it was hard to sympathize, I don’t know if that was my mental health issues taking over or if I’m just tired of him entirely. We have always had a good and healthy relationship and have always respected each other. Our sex life has been dull/nonexistent, but that’s mostly my fault because the birth control I was on destroyed my sex drive. Since coming off it I’ve been ready to go constantly and he just seems uninterested.

Anyway, to the conflicting stuff. I’ve been getting some male attention (which I usually hate and automatically dismiss) from an older man that I had worked with in the past. We are good friends and share a lot in common but sometimes the conversation goes a different way. My problem is, is that I like it. I think about him all the time and end up disappointed when he doesn’t text me back. There’s serious sexual tension going on here that I just don’t share with my SO.

I don’t know if I need to end my long term seemingly perfect relationship and just live independently and freely to find myself, or if I should try to work on it, but I don’t want to a lot of the time. It’s just upsetting that after putting all this time and energy into something that it’s just slowly fading away. Has anyone in long term relationships had this issue? I just want to feel something again.