What Sera demands is selfish, childish and inconsiderate among many other things but it's not even close to absue!! How can you seriosuly even consider this absue!?
Quite easily.
Sera is asking a Dalish Elf to renounce her entire culture so they can contiue their relationship. Now lets think about this for a second, to the Dalish their belief system is everything to them, it is not only their beliefs, it is their identity. Without their beliefs they are nothing more than city elves.
Sera isn't asking an elf inquisitor to just give up her beliefs, she is asking the inquisitor to give up her entire identity or else she's leaving her. Could you imagine for a second being deeply in love with someone and then that person asks you to give up who you are or else they'll leave you? It's a form of emotional abuse, it's creating an unfair ultimatum and placing emotional distress on a loved one for no good reason.