A friend of mine was in the exact situation... however, this was at work, so they only saw each other 8 hours out of the day. But my friend fell madly in love with a guy, who was straight (or so we actually think), and very... weird. Anyway, this same guy now works elsewhere, and it has been better for my friend, who suffers from depression.
If you do want to tell him, the timing has to be absolutely right. Beforehand, I would highly recommend coming to grips with your sexuality. I am seeing where you come from here, as I had relationships with girls in the past, and just started coming out two years ago. Right now, the important people in my life know me for me, and that is fine with me.
If you tell him now, it may be excruciating. Like I said, coming to grips and accepting you for who you are is more ideal at this point.