She (along with Isabela) are the only companions in DA2 to ever even mention their sexualities outside Hawke attempting a romance.
If a core part of Aveline's arc is her marriage to Donnic, and a healthy handful of dialogues and banters are largely sexual conversations about her bedtime exploits with Donnic, then her sexuality is, by definition, a core characteristic. Heterosexuality or homosexuality or whatever has nothing to do with it.
You can make whatever assumption about her sexuality you want, but until her sexuality comes to the forefront, as it does in Dorian's, it is not about her sexuality.
You can noodle it around all you wish. There's a big difference in talking about you liking men only and just showing that you like men. One is specific and excludes all other possibilities, the other doesn't.
You wouldn't know Merrill was bisexual if you only played as male hawke. I didn't know until much later when I read about it.
You are just bitter because
LOLOL, Let me stop you right there... I haven't taken a single bit of this seriously... You'll be hard pressed to show I'm bitter.
Meanwhile you're sitting there being passive aggressive mentioning "the same crowd" mocking people as if we don't know who you're talking about.
Yep, I'm the one that's bitter, ROFL