You just can't win.
EDIT: fun fact! That elf dude talking to Zevran in the last one was supposed to be Taliesen, because I was convinced Taliesen is an elf, not a human dude. I know now because I've met him, and Zevran told him to go fuck himself AW YISS GO ZEVRAN. Sooooo yeah that's Taliesen drawn by somebody who has read about his role but never seen him. END OF EDIT.
I feel like I should mention a few things (spoilers again):
I know Zevran can stay faithful, and when he does, he SO does- ohhhhhh dear god Zevran stop ruining my heart already, it's been about a year since I played that game for fuck's sake, why can't I get over things- and also, for the sake of honesty, I haven't played DA: Origins long enough to even see if Zevran would betray me or not, and PRECISELY for that reason, because even the thought it could happen would tear me apart. Actually, Zevran is the main reason why I still consider getting back to that game just to FORCE HIM TO LOVE ME GODDAMMIT YOU WONDERFUL SEXY BEAUTIFUL CHARACTER YOU. The only elf I love. Sigh.
Aaaand I know that if you tell Bastila you don't, in fact, love her, that doesn't stop you from saving her, although I think it requires some persuasion that way? Anyway, that's what I did, not-romanced her. I stuck with my ideals to the end. You know. Ideals of not romancing Bastila.
Anyway. Yeah. BioWare is reall really great, just... overprotective of my character's social life.