I have a straight friend in college whom I crushed over a bit. I had internet access in my dorm room, so he would come over at night and use my computer to look at naked women, and I'd usually sit there pretending to be interested in the women while trying to be subtle in my eyeing his nudging the bulge in his shorts.
During each of these very long sessions (this was 1996, where each jpg would load.. very.. very.. slowly..), I'd be wondering in my mind if he was interested in crossing a line with me. Just the two of us, my roommate gone for the weekend, the locks bolted shut, us both quiet as mice, not answering if the phone rang or if there was a knock at the door. I could swear that he was.. eye contact held a bit long, awkward silence, tense breathing. But I was far too scared to do anything about it.
When I came out later on, he was a bit freaked. But then he began to hint to me in private that he was curious. It culminated in him going out to bars by himself, not telling anyone, picking up guys, lightly messing around with them (everything but all-the-way), and then backing away from it all. This "phase" lasted for a few months. He ended-up marrying a woman several years after college and now has three kids. On the rare occasions when I see him, I still swear I can see the gears in his head, turning, thinking.
I still regret not making a move, but at the same time, it makes me smile. Just knowing that he was tempted. Just our secret.