Yeah. You tell them.
I was in love with a good friend of mine for three years (it started literally as soon as I met him), and I told him maybe two years later? Although I'd be very surprised if he hadn't already known since all our friends knew about it.
Anyway, he said he didn't feel the same way (which I'm not sure I still believe; he was the king of mixed signals), and we stayed friends but last year we started to hang out a lot and I realised I was still in love with him and I had to completely break it off.
So believe me, no matter what happens your mental health will be better off. In retrospect I am so glad that the aforementioned and I didn't end up together.