I feel like there has to be multiple skeletons in his closet. I think the most likely scenario is that he got in trouble a long time ago for something involving children. Adrienne knew about it but thought perhaps he had change and settled down with him. But the second she found out she was pregnant reality slapped her in the face harder than Patrick surely had on so many drunken nights. The thought of her child being around Patrick, knowing his past and what thoughts must go through his thick head. She just couldn't let it happen. It's the only thing that makes sense and is why the second she found out she was pregnant she demanded a divorce and his loss of parental rights. Patrick immediately signed knowing that he is far too dumb and immature to raise a child. It may very well be the only decent thing he's done in his life.

Also it's totally coke-can-cock Jonathan's kid anyway since he plowed Adrienne's bean field every night while fatso was out drinking and arguing with people on Twitter.