There are situations where buying a house is the only option that really makes sense - in a lot of places the rental market is either completely off the wall unreasonable or doesn't exist, so if you're at the point you want to live together buying a house may seem more logical than paying twice the money to rent a worse place, even if you aren't really at that level of commitment yet.

I still wouldn't buy a house with this guy, but if "buying a house to live in together" is the most workable housing option in your market, then your options are buy it together, or have one person buy it and the other one pay rent, and those are both bad choices.