Diddy -- My Baby Mama Screwed Me and the Bank Over

Sean Combs didn't screw over his baby mama by allowing her home to go into foreclosure -- turns out she's the one who allegedly screwed HIM over by flaking on the payments.

TMZ broke the story ... Diddy and Misa Brim took out a $712K mortgage on a house she and their son would live in, but the bank claims monthly payments abruptly stopped in 2010, and now the house is destined for the auction block.

On the surface it sounds like big, bad Diddy turned his back on Misa, but we've obtained a legal doc that discloses there was a side agreement in which Misa clearly says SHE's responsible for paying the mortgage. Diddy's only involvement was putting his ass on the line so she could get the loan.

According to the agreement, Diddy claims if he had to pay to keep up the mortgage payments, she'd be responsible for paying him back. And he says he paid more than $28K to cover her, and he's actually sued her to get the money back.