› firstname.lastname@example.org 
Greetings. At the tender age of 12, I discovered my father's porn collection and the joys of masturbation. At 14, I can remember inserting my parents' dildos up my anal cavity. Now I often will look at transsexual or bisexual pornography and enjoy it thoroughly until the point of ejaculation, but afterward I'm somewhat disgusted with myself. I only date women and find myself attracted to men only in the way of a circumstantial sexual kink.
The experiences I've had with a man and a transsexual were both unfulfilling, starting as a hot, steamy romp and ending with me saying, "I'll never do that again," or "This isn't for me." Yet I find myself scanning Craigslist personals looking for hot TS women, well-endowed daddy types, and couples looking for that young bi-curious male, sometimes sending aimless e-mail I don't expect anyone to answer.
Is a trip to the shrink in order? I'm only 21; maybe I'm just defining my sexual identity. Still, it seems a bit selfless to be a student, friend, and employee all day yet have this undeciphered sexual attitude present at all times.
You didn't mean "selfless," you know; you meant "without self" undefined, maybe hollow. "Selfless" means, like, spending all your holidays down at the soup kitchen: unselfish, as opposed to self-free. You aren't worried that you're too nice: you're wondering if maybe you don't even exist. Relax. You do. You're just experiencing the juxtaposition, both exhilarating and potentially alarming, of being very young, hence somewhat unformed, and open to experience. Empty mind + open mind = blown mind, but not permanently. Don't worry.
Also, don't start your letters with "greetings." Seriously, it makes you sound about 16, hopelessly adenoidal and socially maladjusted, like you'd better make those assignations via Craigslist because nobody but a really determined predator would approach you once they got a look at you. Don't want to sound like that? Never ever say "greetings." Say "hi." And while we're at it, stand up straight.
I don't see any reason to waste a therapist's time or your own trying to figure out why you, a young, highly libidinous man living in a fairly old, highly libidinous city, would be interested in sexual exploration. The phrase "fleshpots" was or at least could have been coined for this place. Not only was topless go-go dancing (more or less) invented in San Francisco, so was Craigslist. So there you go.
I think one of the most important sexual experiences one can have here, or anywhere else regularly described as having "fleshpots," is getting to come out as what you were. You sound pretty much like a straight guy with kinky fantasies to me, and as such you have plenty of company. Hardly anybody ever gets around to doing all that weird stuff you see in porn. And although there are obviously real-life tranny chasers and such, there are far more married, monogamous guys with large collections of shemale porn. I think you're on a journey of self-discovery that will end with you standing just about where you started, but with a little more insight. But try not to end up there with a case of hep C or anything while you're at it, OK? I don't get the sense that you know all that much yet about what kinds of dangerous agents, human or viral, might lurk out there in the, you know, fleshpots.
I also didn't get the sense that anyone was actually answering any of your aimless e-mails (perhaps you're starting them with "greetings"?). But I do urge you to think through what you would or will do if you happen to catch a live one. Perhaps it would be wise just to read the personals for a while and have a nice, safe, contemplative wank when you find something that strikes your fancy. You've already discovered that at least two of your experiments were, for you, better left to the imagination. I can't help but think that there are many more out there just waiting to disappoint you.
Go slow, son. There's no time limit in operation here. As to your last question, there's no contradiction between being a student, a friend, an Eagle Scout, and whatever else was on your list, and having a great, honking, perverted imagination. What do you think your friends are thinking about when they peruse Craigslist? It ain't secondhand furniture or a really great cheap babysitter not yet it isn't.
Andrea is home with the kids and going stir-crazy. Write her a letter! Ask her a question! Send her your tedious e-mail forwards! On second thought, don't do that. Just ask her a question.