Please accompany me for a moment on a thought experiment. By the end, you might just be able to make my point for me.
Imagine yourself as a virgin, who has never had sex before. (Some of you may not have to imagine. Others will have to think back to grade school.) Now, picture that one Friday night you and a classmate find a quiet room somewhere, get naked, and have absolutely mind-blowing sex.
After finally getting home on Sunday night, you lie in bed, no doubt thinking about the experience and how your life has changed. You might fret and worry over the taboos you've crossed. You might be relieved at passing another of life's hurdles. You will almost certainly be thinking of the person you had sex with, and wondering if you can do it again next Friday night.
Now, with that thought firmly in mind, think about what would be different if you were a different gender, or if your virginal mate was a different gender. You'd still be thinking about them. It would still impress upon you the "wow" of sex, and should you and your virginal partner seperate you would likely seek out a person of a similar gender and orientation to your virginal mate.
Humans are designed to want to fuck whatever we first fucked pleasurably.
In fact, the underlying principle goes even further. Those of you who aren't finally re-taking Psych 101 this semester can probably list a litany of other instances where humans seek out repetition of situations they enjoyed.