i think you're always going to want to be the biggest or best in bed or best looking or best oral sex or most intelligent or most successful guy your girl's ever been with. just like she's going to want to be the prettiest, sexiest, best in bed, nicest breasts, tightest pussy, funniest, one your friends and/or family like best. that's just human nature. most of the girls i've been with, i've been the biggest they've had...and if i haven't, they've made little exceptions to stroke my ego. "Oh, you're the longest" or "thickest i've ever had!" "wow, that's the biggest white cock i've ever had." "well, i've only had one bigger, but i just blew him, so you're the biggest to ever be inside me." my last girlfriend and i broke up for a while, and in the interim we'd both slept with other people. and when we got back together, we eventually found out. i told her the sex was good, but not nearly as amazing as it was with her (which was the truth)...and she told me the sex she had was unsatisfying and she had just been drunk and bored while out with a friend one night and that, yes, his dick was smaller than mine. a few months down the road, i cracked some joke about it and she came clean that no, in fact, he was at least as big if not slightly bigger than me. and that just bugged the hell out of me. she assured me that that was the only thing she fibbed about...the sex with him was totally unsatisfying and unimpressive, she hardly got aroused let alone orgasmed and he didn't even bother to go down on her. and that i was still the best sex she'd ever had. and yet, for some reason, that little fact...that he was SLIGHTLY larger than me...just kept bugging me. and i realized...we like that feeling of accomplishment with our significant others, that notion that we are the biggest, best and brightest that they have EVER been with. and though i was still the best...i was no longer the biggest, by a fraction of an inch. how ridiculous is that? it's not like he had some monster cock and made her cum just by looking at her or something. i had no reason to feel at all inferior to this guy. but i let that doubt creep in. and it took a while to get over it.
if you love the girl and she loves you and the relationship is going well and the sex is awesome for both of you...then the rest of it is just gravy. worrying about it or fixating on it is just neurotic (which of course means we're all going to do it...again and again and again...lol).