Re: question
A good point, and I think it's neat to play with exploring her development without dismissing that central aspect of her relationship with her.
Both canon and interviews (and drafts of the pilot, and just about any source you can ask for) have confirmed he likes a challenge, and the danger of it - this is partially why he goes for ladies who are taken or who are, supposedly, out of reach, and why this is usually an incentive rather than a turn-off for him.
You can say that reflects here in that he liked Arthur, who rejected him initially, is a king, is from another land, is dead, is taken, and basically can fill up an "unobtainable" bingo all by himself. Or Jamie, who obviously keeps a lot of things from him and where the difficulty lies on that chance for an emotional connection.
On a less "Aramis please" note, he loves motherly women and mothers, period, he's drawn to people who are sad or have issues of some kind because he's a very nurturing and caring~ person and he likes to get all mother-hen on them. His lack of judgement (over things like titles, or origins) also means he meshes well with people who could have self-esteem or identity issues. Again, see Arthur and his million insecurities/identity struggles, see Jamie with her shady as hell past (a lot of which he doesn't even know about lol), see (Isabela is very right about this one) Snow, who he'd be stupidly in love with if he could see himself having the most remote of a chance with her, and who has all that sadness and traumas from her past and issues regarding parenting.
Turn-offs would be disliking Porthos in any way, hurting Porthos in any way, being the kind of person who could dislike or hurt Porthos in any way... Hating children, arguably being aggressively atheist or anti-catholic (he's a bit more lenient with this, and he's not overly preachy but if it came up a lot he'd probably not like it much), being violent or hateful or in any form gross towards women, and then obvious things like idk being homo/biphobic, hating soldiering, being Alice being involved with one of his friends (unless that's okay, see: Robin)...
Since we're talking romance, what're your views on Elsa and that? I'm sure on her part it's probably more like PLEASE STAY AWAY FROM ME, but I wonder how you view her/any potential romantic shenanigans just ramble about her and Bucky, really.