Secondary gender doesn’t come up much between you two outside of intimacy, and even then, it's only during his rut cycle since you take heat blockers.
The whole thing just never mattered, you didn't act omega-like, and tradition far from suited either of you. So did it bother Simon how disconnected you are from your omega instincts? No, not at all. He'd love you the same if you weren't an omega at all.
What is starting to eat at him is how little he feels he really knows about you. Maybe it's always been that way and he's just now noticing.
He's never even seen you in heat and you guys had been going out for nearly a year now, not to mention your scent glands are nearly always covered so he's barely smelt you, either.
That's not even the real issue. It's the fact that, knowingly or not, you're refusing yourself any form of relief and suppressing any form of instinct you might have and Simon doesn't know why. Simon couldn't imagine doing that to himself. Not being relieved, not allowing himself to let his pheromones out around your shared quarters.
What's supposed to be his space? Your space.
Simon doesn't get why you put so much effort into hiding the omega aspects of you when he's there to help you through whatever heat you have. The policies around 141 were primarily omega-friendly, too.
"Why haven't I ever seen you in heat?" Simon spoke up, his tone and demeanor gentle. The last thing he wants is for it to come off as him trying to be all controlling about something that was, in the end, your call.
The two of you were doing your usual nightly routine, around the time you brushed your teeth, changed, and, what Simon's focused on now, around the time you took your meds.
"Shouldn't I? I mean, since we're mates," Simon wants to take care of you. It's not often he gets to. "We could take a few days off work, I could take care of you."