someone who’s been raised in a home where too much has been done for him.
That doesn't really make sense though as he stayed with her plenty of times and never pissed all over the bathroom before, surely if that was the case he'd have been like it from day one?
My personal take on it is that OP got herself into financial difficulty, may have even lost the house anyway if it was that bad, so her boyfriend has offered to move in, pay a lump sum (which solved her financial issue) and go on the mortgage to protect his interest, sounds like a win win for OP if they were planning on living together anyway.
Except she has put all her trust in him and his 'friend' and they have taken advantage of her in setting up a mortgage that benefits him more than her.
And now he is joint owner he has realised that the honeymoon period can be over, she can't kick him out so he can start acting like the slob he was always intending to be eventually, and rely on her to do everything for him, including cleaning up his piss.
He may not be abusive in the physical and emotional sense, but he has lied to OP about exactly who he is and what he is like, until she is too far in to do anything about it, a common tactic of abusers, and now he is being his true self and doesn't care that he is disrespecting her and their house.