When she basically asks you to deny your beliefs and your heritage to continue the romance then yeah you lose alot of my respect. Just like ugh the selfishness of it all, I can't go through that scene again as an elf Inquisitor.
Actually this happens a lot irl. Sera doesn't date elves who believe in dalish gods. Clashing beliefs and all that. She basically tells you the relationship won't work if you both belive in different gods/religion so she saves you the trouble. I personally i'm atheist but i honestly wouldn't date someone who strongly believes in a religion because that could mean our beliefs would clash and bring a lot of trouble in the relationship (though i can respect their beliefs. the problem lies in them if they'll respect mine). Then again there are ppl who are happily together and respect each other's beliefs, but a rare thing. Sadly.
Though it's odd because this should've been cleared out from the first time you flirt with her and tells you that she doesn't date religious elves before moving on, instead of going almost at the end of the game and drops the "me or that" bomb.
Things like these make me wish she wasn't available to elves tbh.