Ma'ar's thoughts are a tangle of half a dozen different threads; insofar as he's a bit tipsy, it mostly means that he's less focused on a single one, and there are more emotions floating around with unclear connection to the rest.
He hadn't realized he was being nicer to her? He supposes he feels more relaxed around her, which is maybe a little about sleeping together, but is more about the sparring, and more than that about...something subtler, something upstream of all that, which he has a hard time pinning down. It's whatever made her able to notice that sparring would help his mood, and motivated to offer it, and it felt like that was the first time he really started to see what it meant, that her caring about Mhalir transfers to him. And what 'caring about someone' means, for Carissa, who's so cautiously guarded in all of her emotions and attachments.
He doesn't think he has expectations here, not of her. She could at any time decide to leave, or be pulled away, or decide she isn't actually interested in him that way, and - it would be fine, he's an adult, he won't get stupidly upset no matter what happens.
The thing he wants is - very specific and even he isn't quite sure what it is, except that he wants it more, rather than less, after yesterday. It has as much to do with how the party felt, Mindspeaking her at random to share his commentary, as it has to do with sex. Though the sex was very good. He's been with a lot of women and sometimes it's good in that way and usually it's boring and he thinks about magic during, and he's never really understood what makes it one way or the other. Either way that's something he's fine with or without, it's nice but he's not really planning to chase it, especially not at the expense of his strategic aims.
...but there's something else that he wants, he's starting to think that maybe he wants it very badly actually, and it's - related, at least, to how Carissa is with Mhalir. Partly how they share her body and magic in such a beautifully effective, efficient way, but it's not exactly that he wishes he were a Yeerk and could do that, it's - there's a thing there...
(Ma'ar is feeling vaguely apologetic that his thoughts about this are so murky, it'd be easier if he were sober. Though possibly if he were sober it would feel too self-indulgent to dive into his confused emotions at all.)