Making an Offer with a Partner Have a Question...

[Luke Carl]

So I found a deal and a partner to go 50/50. Ready to make an offer. 

If I make the offer and go under contract with my name... How does that effect the mortgage being in his name? Or does the contract have to be in his name? At which point I would need a contract with him on the side up front so he doesn't run off with my deal?? 

How does this part work? Better to ask stupid questions now I suppose. My realtor had no clue.... (i know, i know) 

Thanks