I'm not exactly a fan of Adrian but I'd say this ability to trust Erin, respect her judgement, and generally not equate love with ownership is actually pretty cool.
He's asking remarkably few questions for what should be a real big deal. Plus, I know the relationships aren't meant to model real ones considering magical mind control is involved, but "I want to open up the relationship. I already have someone in mind." is a HUGE red flag. And, given magical mind control *is* involved, I don't think "love is ownership" is out of the question.
I'm not sure what happened to "only him, forever", but I suppose, as a get-out, we never saw Erin being given that programming. We did see a load of commands given to Marliese and that wasn't amongst them. Regardless, we know Erin has been affected by her encounter with Jakob, so maybe that's what happened to it.
You're right in that we never saw Erin being given that programming; but it did happen to Caitlyn, and IIRC she was asking about other guys even before she got zonked with whatever Coates and Astrid have in their closet. But perhaps we don't have the full context of what that programming meant and what has happened to Caitlyn.
Adrian does appear to have slipped out of Evil Adrian mode without any transition that I've discerned, or any acknowledgement that anything happened. I'm not really sure what's going on there.
Unfortunately the characterization seems a bit unclear. I'm trying to understand what his motivation is, anyway, and coming up short. He mostly just doesn't seem proactive enough. He might be able to learn a bit from Daffyd, tbh.