One Fuck-Up At A Time

In-game they can sleep with each other, which is basically the foundation of the normal Tav/Astarion romance. Lae'zel saw him during combat and got horny, who knows. Astarion who's used to luring people with his charms, takes up Lae'zel's blunt offer because she's a strong hardened warrior that can provide protection and be a worthy ally, and he doesn't know how to say no. Navigating the complications between one who wants to be seen beyond as a sex object, and one who comes from a totally alien culture with no concept of love/family/connections and only sex is honestly really compelling to me. It's a transactional, mutually beneficial thing with no emotional expectations. Once you get past the skeevy rockiness of their early relationship, I really like the idea of them slowly seeing something past the exterior and realizing they may have harshly misjudged the other, an unspoken friendship blooms, and in comes the realization that they are essentially loners longing for kindness and a comforting touch in the most desperate of situations.

Lae'zel is prideful, direct, has no sense of courtship talk, and doesn't hold back her thoughts the slightest--she's not sweet/agreeable and what you see is really what you get, which I imagine would be disarming for Astarion who's used to vacuous flattery and has difficulty trusting others. But she's also insanely protective, passionate, loyal, and an initiator-- every romance scene is triggered by her first and she's always showing effort towards her relationships, which would mesh well with Astarion who does need someone to nudge him.

She doesn't purposely suppress her feelings, she's just simply at loss at how to express them sometimes due to her wildly different upbringing. She stops the sparring match you agree to and an easy vulnerability slips instantly out of her: "I don't want to hurt you. I want to protect you, and for you to protect me." and "Thus far I've taunted you, devoured you, battled you. Now I want more than anything to soothe you." are romantic as fuck and Astarion of all people really needs to hear that tbh.

Astarion is also someone who struggles with reinforcing his boundaries, and a key theme in Lae'zel's romance is that she encourages and wants you to challenge her and learn to stand your ground. It's not gentlest method, but hey, relationships are about having to make an effort to learn each other's language.

I think he also would take pleasure "educating her on the matters of Fay-run" (I believe there's a whole banter with him teasing her and teaching her pet names) and would get a kick out of coaxing Lae'zel out of her shell with her shyness at showing public affection, and making her blush. Also it simply would be fucking funny to see Astarion who's used to easy seduction, trying to pass a persuasion check just to get a smooch and generally having to work to earn regular kisses from Lae'zel lmfaooo

Lae'zel also initially struggles to see her chains as chains. When she learns about Vlaakith's betrayal, she copes instantly through denial and shuts it down. Astarion is NOT having it and calls her out, he knows her well enough to recognize that she would value blunt honesty above all.

I imagine he also despises her lack of self-preservation, the way her entire identity is tied to duty and being in service of others, and doesn't understand her desire to still help/liberate the people that want her dead and are hunting her down. He wants to make this duty-bound soldier realize that looking out for herself, and putting herself first may not be the worst thing in the world.

They're so similar to each other but are also polar opposites in some ways that make a more equal, balanced romance I think. It's not a simple, one-sided, feel-good "she/he can fix her/him" fantasy because both of them have to earn each other's love, actually cut through the other's flaws, and actively motivate each other to be better versions of themselves.

They're not at all the other's ideal guiding hand. It's rough, jagged, and imperfect, but that's how healing goes. It's so far from being the healthiest relationship -- but even if their belief systems differ, their moral compass does often align. I imagine it's a slight relief for them to have a partner where there would be less shame and judgment when they expectedly, occasionally slip up and fall into their bad habits.

Also, man, the "You showed me the betweens and beyonds. Beyond war and peace, beyond passion and obsession, most importantly, you showed me freedom.", "First you were my wound, now you were my cure.", "But you saw something else in me - someone else I could be. Someone who could break the cycle of power and terror that started centuries ago.." lines really hit hard when applied to them.