Married and have devastating crush (bordering on obsession) on someone else

I developed a crush on a friend (35/M) and it is killing me (42/F).

I have been married 12 yrs with kids and have never been happy in the marriage. Husband is lovely, but I just don't feel the same way. Have been very vocal about this throughout course of marriage as feel we were good friends who got married.

I met someone recently and the crush I have on him is debilitating. We became somewhat friendly. We have a lot in common and I feel very comfortable and at ease around him. We don't really see each other a lot, but I find if he doesn't text me or answer me on messenger app that I get extremely upset and then am in foul mood for the rest of the day. I wake up thinking about him, go to bed thinking about him. I have essentially checked out of my marriage and I just don't know how to get over this. I think the feelings are somewhat reciprocated with my crush, but he never said anything, I think bc I am married, which I respect. Do I tell him? He is younger than me, so I am not sure even if I were available he would want to pursue anything with me, but I feel like I would feel better knowing he felt the same way.

I know he cares for me, he has essentially said so, but I feel like he is cutting me off because I am not available and I just want him in my life.

TL;DR : crush is consuming me and I don't know what to do about it.