My boyfriend and I are in an identical situation as you are, so I just want to "this" your comment and add a few other notes.

He pays a little under reasonable market rate for renting a room in a house in my area.

Same. My boyfriend is a grad student (with a stipend) so his rent is pretty much market rate minus a little bit that is reasonable within his stipend.

Note that my mortgage never comes into this. He's not "helping" me with my mortgage-- he's paying a fair rate to live here.

Exactly this. What my boyfriend pays has zero to do with what my mortgage/insurance/taxes cost me.

He helps me with repairs because he wants to, but I pay for everything.

For minor things like a new gate lock we need, we're splitting it because it's more of a cosmetic thing that we both want, rather than a repair repair. (Things like this also really don't cost much; will be less than $20 total...). But otherwise yes, I would never expect him to pay for things like HVAC maintenance, etc.

It's my house and I have 100% say who comes over, and definitely who stays over.

We both live far away from family, so it's never really come up. We've been together for 6.5 years at this point, and are really just waiting on him to finish grad school before we get engaged/married/etc. But at this point his family feels like my family. And to be fair, I'm the one with the crazy relatives, not him, so I can't see why I'd ever need to pull a "my house, my rules" thing in my particular situation.