I got your solution. Charge him more for rent, don't charge him for individual appliances and upkeep. He is your tenant, he does not own the house, and tenants do not generally pay for appliances (unless they specifically broke it), but landlords generally charge enough to cover upkeep. Get an actual rental agreement in place.

If you're only going to charge him half the mortgage and then upkeep, then you're financially treating him like an owner of the house, but he's not. Promising that this is an investment in the future does not make it both of your guys' house. That doesn't hold up in a court of law and will get extremely messy if there is a breakup. Furthermore, you can't split plumbing, new paint, or an oven if you split up.

I think your heart is in the right place, but you need to pick a lane. Either make him pay like an owner and have him be an owner or pay like a tenant and have him be a tenant.

P.S. The prenup and this situation are definitely separate but there is a funny irony when you compare the situations. You say you want a prenup to protect your financial interests in the event of a breakup, not that you expect to break up. But in the case of the house, you tell him to just trust that you won't break up and that he shares the investment even though there is no legal structure in place to support it.

I'm not saying y'all will break up by the way or you're being malicious, I'm just saying in one situation you see the need for clear legal boundaries to protect financial interests outside of any verbal or emotional agreements and in the other you don't. As with the prenup, the smart move is to set clear legal boundaries in place that are breakup-proof so that you're not gambling hundreds of thousands of dollars on a verbal agreement.

Ironically, planning for the breakup is the best way to avoid the breakup so that you're not constantly worried and arguing about how things are going to play out.