I (M21) think I'm massively sexually attracted to my friend, now also manager (M34)

A throwaway because I am 99% sure he uses reddit and I can't bear the thought of this getting out.

So I(M21) have a friend. We met through a mutual hobby a few years back(let's say I was 16-17) and we got along fine. We weren't super close, a hi here and there, but as I've engaged in the hobby more we've gotten a little closer.

The catch, I both have a girlfriend who I love and adore, and mostly consider myself asexual(aka haven't really ever experienced sexual attraction). However, for some reason, over the past six months I can't stop imagining myself and him engaged in less than chaste activities, to the point he once walked past me and I swear it felt like I genuinely blacked out for a minute. This is compounded by the fact that he recently helped me get a job at a spot where he's managing since they're short staffed. I'm losing my mind, it just gets worse every time I see him, and it's not like I can say anything. I'm pretty sure he's straight, and beyond that he's more than 10 years my senior and I love my girlfriend.

I wish I had more to add, but I just needed to shout this somewhere, anywhere.