I just don't want a roommate situation.

Buy a place and get roommates, where you are in control and can manage it yourself, etc.

The setup: Roommates A,B,C signed lease and roommate D agreed to move in a month later and add himself to the lease.  

From personal experience, the issue he had may not have been with you and your girlfriend, but with the "third wheel" roommate.

The Story: My college roommate and I were just getting into the real estate investing game 1 year after graduating college.

He moved out a few years ago but remains my craziest tenant story, followed closely by several others, like the peyote cult leader who grew peyote in his closet (which he claimed was legal because his peyote cult had official church status) and tried to stab his roommate one night during an argument at a backyard bonfire party.

One just moved out so I need to do a new lease agreement with the tenant staying and their new roommate... the tenant staying just got a new girlfriend pregnant.

Rent a 2 or 3 bedroom with your gf, with permission to sublet to a roommate or to AirBnB the extra room. 

Credit is bad for these two roommates, but the first payment was received early instead of skidding beneath the deadline or asking me for considerations (funny story, had an applicant ask me for considerations before move in - eventually denied tenant).  

What are some great questions to ask beside the normal reference, deposits, etx.. that you wouldn't think of to ask potential roommates or tenants that would help you determine if they might be a problem later down the road?