You shouldn't get stressed out over normal sexual curiousity. If society didn't have such rigorous rules regarding human sexuality, it would be accepted that everyone is to some degree bisexual. Any guy who say he's 100% straight and has never even had the slightest curiousity or desire when it comes to other men is lying.
You might find you love sucking cock, even if the guy it's attached to does nothing for you. Maybe you will meet a guy with a dream dick that you fall for. It could be a one time thing that you don't enjoy, or a new world of possibilities. Whatever way it goes, you won't know unless you open your mouth and swallow a sword.
Regardless of the outcome, nobody has to know anything about your sex life unless you want them to. Be as discreet or open as you want. Are you afraid of being gay? Again, nobody has to know. If you do find yourself falling for a guy, just go with your instincts. It's your life, fuck what anyone else thinks. There is a reason some guys marry women and suck dick in secret: sucking dick is so incredible that you'll risk anything to do it!
As for your fascination with big dicks, keep in mind that what you see in porn is not exactly reality. Sure, a think 10" tool looks tasty, but it's WORK sucking a big dick. Your jaw will ache, trying not to use your teeth will be tough, he might be rough and shove it all in (and God help you if he fucks you hard without prepping your hole). I hate getting hairs in my mouth, so a guy that trims his pubes is great, although the shaved bald look turns me off (they look like they have yet to hit puberty). I hope your first experience bobbing is a great one, a bad one will ruin it for future chances. Make sure he's got a size you can handle as a novice before you move up to the big boys. My joy is in deep throating, guys love getting sucked to the balls. Once you deep throat a guy and suck him to a roaring orgasm, he will want to see you again (unless he's a douche). If all you want is no strings, no talking, no physical affection, you can always try glory holes or find guys who just want head online or at gay bars.
The best piece of advice I can give for sucking on some guys piece is what was said to me by an older mentor: suck his dick like it's your dick. Do to him what you like having done to you. Lick and suck his balls as if it's your last meal before execution. Lube a finger or two and play with his hole! Massaging a guys prostate will drive him insane with lust, and cause a much bigger cum than usual. Every guy I started off fingering eventually was taking one of my vibrating dildos with pure joy.
If you're uncertain you will want to swallow his load, eat your own cum first. There are subtle variations in taste from guy to guy (red meat, alcohol, smoking makes cum bitter. I'm a vegetarian and guys often tell me my cum is delicious). Tell a guy you want him to cum on your face, guys love givig facials!
