Welcome to JUB!

I'm going to have to sort of assume there's nothing in the backstory to contradict what I'm going to say, so I'll lay it on you to correct me anywhere where I might have gotten it wrong.
I disagree with WYS. I think you do have a good friend here. One who has tried, in his own way, to let you know "Look, you're gay (or bi). That's fine." But you've tried hiding it, you've denied it, and even when presented with point-blank evidence and an accusation, you brushed it off with something along the lines of "well, I'm not really anything". This isn't a brain buster. If you're attracted to guys, you're gay. (Or, if you're attracted to both, you're bi.) That's it. It doesn't matter if you like Broadway musicals, or ogling big muscular guys, or talk with a "gay accent", or fantasize about getting fucked in the ass.
If you're attracted to guys, you're gay.
Yeah, he's being pushy. But it sounds like maybe you need pushing. You say "I've been just fine for this many years", but gargoyle calling bullshit on that one. Living in the closet, not dating anybody, and not coming to grips with your sexuality isn't "just fine". You're supposed to come to grips with what you want sexually, then go out, meet some people, date, get laid, and start a relationship. Not put it on perpetual hold. So I'd say take this situation, and turn it into a positive. Start dealing with your sexuality. Not as something to be shunted aside, but as something to be discovered and embraced. We can help you with that.
As for your friend, don't write him off. Send him an e-mail. Be brutally honest with him, and with yourself. I'd say something along the lines of this. "You asked if I'm gay or bi. And honestly, I don't know. I might be. My sexuality is something I've intentionally not dealt with on any level for many years. And this situation, and your messages to me, have sort of dragged me into a place I really never wanted to go. But maybe it's time I did deal with it."
Lex