You are still in what I call the "wow-I-didn't-realize-how-sexy-some-guys-look" stage.
Given today's attitudes towards men appreciating other men, sexually or otherwise, it's not surprising your mind is allowing you to fantasize. You don't have enough information - or experience - to know that you'd like this, other than that you appreciate "fit" guys. I mean, look at the commercials on tv: some straight guy sits next to Michael Jordan on a plane, and, because they wear the same underwear, proclaims, "You and I could be brothers!" To which, of course, Michael Jordan says, "no, we couldn't." And the guy continues to insist they could. Straight men have their own version of attraction to other men, but usually based on hero worship. I see no reason why that couldn't be taken further to a straight guy who idolizes Michael Jordan thinking, "Wow, if he made a pass at me, how would I react? I WORSHIP this guy! He's the greatest basketball player EVER!" It's not hard to imagine straight men melting down when one of their heroes even just puts his arm around their shoulder. You can SEE them beaming, and later on, when they're relating the story to their buddies, their buddies go, "You LUCKY bastard! Fuck, why couldn't that have been me?" The attraction may not be sexual, but it sure is a kind of romantic ideal.
Some of homophobia comes from a fear of being less manly and the other stereotypes associated with even liking other guys (and how many of us didn't worship our older brothers? That's where it starts. I didn't worship mine, but I sure looked up to him). In fact, in Britain, an article recently came out that 39% of British men not only kissed their male friends, but had actually made out with them. And the researcher was shocked, because, well, wouldn't that be "gay" as he put it??? (It wa also pointed out that American men were pretty far behind in that respect of demonstrating affection. Ah, those crazy (and neurotic) Americans. We shoot each other, but kiss another guy? GOD FORBID!!!
In your case, a sense of "Hmmm, I wonder that it'd be like to be with another guy…" isn't all that farfetched - or even strange. You're of a younger generation, where guys aren't as uptight as guys in their 40s, 50s and 60s. And finding another guy attractive, what with even male actors saying they've tried it out, gives one a feeling of relief, as in "So, I'm not weird for thinking another guy's sexy." I think straight men have always found their straight buddies handsome, and have said as much, although not in a sexual way. Many, many men wanted to look like - and BE - Cary Grant. They saw him as a really good-looking, masculine guy and they didn't mind admiring that he was attractive.
And, if you still like women, too, then you've simply added to, as David Geffen once said, the possibility of having twice as good a chance of getting a date on Saturday night!
You're young, guy. Don't overthink it. Try to relax INTO it and allow yourself to enjoy it without the negative connotations that society has put on men for centuries (exclude the Greeks, by the way). They encouraged the worship of older men by younger ones, including sex, until the younger man was well into his 20s, although it seems, in literature, to have happened more when the man was "a beautiful youth" of 18 or so… Even Apollo was said to have had flings with men...
