HEAR ME OUT
I love the concept of asexual Dex, but I might add a little twist in it, from personal opinion ofc.
I think that Dex has sexual encounters but as his other relationships and basic social interactions, it is not healthy. For him sex is overwhelming—too intense, too much. His need for order and clean environment is freaking out during sex, there is so much fluids, textures, smells, sensations...
But I do think that he still has some. For me, he can have two type of sexual activities: one very primal, and one impulsive. But either are chaotic.
The "primal" one is basically where I put his possible past sexual experiences. I think that he only had hookups, with different person every time, to avoid awkwardness and real social interactions as much as possible. So maybe he'll flirt with a cute waiter and then fuck with them, because it feels hot and sexy in the moment, but that's it, absolutely no romantism in this.
Then the second is impulsive. This one has a tone of emotion in it, but as always it is not healthy. For example, if you do believe in Dexmatt, I think that in this dynamic Dex could actually feel a sexual attraction to Matthew. Not because he's in love with him, but because he is obsessed with him. (Not in yandere kinky way, I'm talking about psychology here). Matthew and Dex have a special connexion through death and violence. Why I called this "category" impulsive is because I think Dex would be very passive through this process. His emotions are taking the lead, against his will.
While the "primal" can be associated with Fbi!Dex, I think the "impulsive" is 100% DDBA!Dex.
Another headcanon I'd love about Dex in sexuality, is that I think he'd be very very awkward after sex. He would need space, a deep shower, a protocol to follow. He would be sweaty, maybe even having a panic attack in some cases. Because again, it is not healthy. For the person he does it with, but also for him. Even if he might enjoyed it, it's in a certain way not very consented for him, it's a form of traumatic respond.
But !!! I do also think that he could have healthy sexual activities, but under very specific conditions he'll need to understand firstly himself—thing he struggles to do.
I think it's for all of these reasons that submissive!Dex makes A LOT of sense. He needs control over his own mind, he needs someone to guide him through it. And in contrast, dom!Dex is also a reality but during unhealthy sex (one shot, quicky, dub-con etc.) I'm not saying these kinks are unhealthy!! Just in Dex's world and life, they unfortunately are, unless it's with someone that really concider him and help him understand that sex is not supposed to be forced, or uncomfortable.
Again, it's my opinion 🫡