Heh. Play the other origins, omg.
The whole game is about you being a Grey Warden. How you become one is dependent on your origin. In some situations, you simply have no choice (i.e. a death sentence). In other situations where you do have a choice, you either voluntarily sign up or Duncan invokes the Right of Conscription, forcing you to come along. It just adds a little flavor. The following dialogue you get in camp allows you to complain about having to be there at all or you can be a loyal follower. Just little things like that.
There are only four romance options available: Morrigan is for male characters only. Leliana (female bard) and Zevran (male rogue) are bisexual and available to both female and male charactrs. Alistair is for female characters only.
You can try to sleep with everyone if you want, but you're going to be forced to choose. (i.e. The females will ask you wtf you're doing with the other person and you basically have to decide who you want to stay with and break up with the other.)
Also the sex scenes will only play ONCE. I don't know why it is. The rest of the game, you only get kisses when you are really asking for sex. There *IS* a mod that will trigger the sex scenes every time for you. The only difference I've seen is that for Zevrhan, when you asked for sex, he'd lean in to kiss you and the sex scene would be implied. In the mod, it just goes straight to the sex scene, no lean-in kissing prelude. Go to
http://www.dragonagenexus.com/index.php and do a search for "Sex Movies Always Play" and pick the race you are playing. (I think the author has to adjust the scenes based on player height/size. My dwarf always had to be moved up to even be kissed by Alistair.)
**MINOR SPOILERS BELOW ABOUT SEXUAL ENCOUNTERS**
If you "harden" Alistair or Leliana during their personal quests (google that term for more details), they'll be more wiling to do a threesome later on in the game when you encounter a female pirate. No sex scenes though -- it's just implied.
If you do the human noble origin and talk to one of the guests later in the study (after running into your mother, but before you seek out your brother), you can arrange for the male or female to "meet you" in your room later that night. (Does not matter what gender you are.) No obvious sex scenes, but they do wake up in bed with you and walk around in their undergarments.
There are more situations like this in the game, but I don't know where they all are. I'd need to find a spoiler site or a thread that detailed this stuff.
***END SPOILERS***