Another noteworthy dialogue happens in the scene where Astarion breaks up with Tav after entering act 3 if he was neglected. He says: "I never slept with you for pleasure alone." So yes, there are several dialogues where it's confirmed he does indeed enjoy sex with Tav. I agree with LiryFire about the Lae'zel matter - she is exotic to him and they generally have a good connection and agree on many things. He's also curious what her blood tastes like.
Astarion lacks the commitment and depth of love that Gale gives.
If you ascend Astarion and agree to his proposal, the commitment is eternal, "until the world falls down."
