I agree with the others. You don't "become" gay. You are or you aren't. Whether you are gay or straight,you will be aware if other guys or girls are attractive (just listen to some gay guys talk about the way some women look). I also agree with Paxiled: once you get it out of your head that one or the other is a bad thing, just be yourself and relax. You are 14. You have time to figure it out. There is a difference between finding someone attractive and being sexually attracted to them (or at 14, just having a crush and wanting to be around them and hold their hand!). I don't think I appreciated what it was at the time, but in hind-site my first real crush happened with a male teacher when was in 4th grade.
I went through this a little older than you are after my first big break-up. It's very common to have doubts about things, and just because you're male doesn't mean you can't therefore appreciate the male body. But that doesn't make you gay, it means you can see. The way to get over this is to stop thinking being gay is a bad thing -- it just is, just as being heterosexual just is.
It sounds to me more like you are worried more about the thought of being gay than really having same-sex attraction. I agree with anxiety860: Just because you notice that a guy is good looking, that does not mean you are gay. So, stop punishing yourself for that and maybe some of your worrying will dissipate. Also, if you were gay, it does seem like you would have had some earlier same-sex attraction. You already know that you are sexually attracted to girls, so that at least should give you some sense that your worrying has an obsessive, irrational quality to it. Perhaps you could explore with a therapist why the thought of being gay bothers you so much?
Chris
All guys think certain other guys are good looking. It doesn't mean you're gay. Being gay or straight isn't a choice. For me I didn't choose to like women I just did. My co worker (who is gay) didnt choose to like men he just did. I'm a straight guy but when I see Brad Pitt. Tom hardy. Or even some guy on the street I can say to myself... Yeah that's a good looking dude.. Doesn't mean I'm gay... If you are gay so what?? What are you worried about? At age 14 I think you would know. Plus you're hormones are likely going crazy now. 14 is when it all about started with me