John, hope you dont mind if i go throug your post in bits. it's too long otherwise (sorry bad attention span).

"Yet, I am in a relationship with this girl, who I just got pregnant (an wanted to at the time, terrible judgement), and now I have zero interest in her and continuously think and picture every single fault she has."

OK, does she know how you feel? are you planning on taking care of the baby when he/she comes along? how are you going to do that? RElationships are very hard. How long have you been together? Sometimes we get to a point where a relationship can't continue. However, lots of long term relationships get to that point cos you become so familiar with each other there's just no spark left and it's up to you to reignite that spark. IF that's what you want.
I read at the end that she's using her right to choose, do you blame her? Do you wish she would keep it? Are you judging her for it?

"I have cheated on every girlfriend I've ever had and don't know why."

YOu do know why. you just don't want to admit to it.

" I use drugs more often than not and would say I have a problem with drugs, alcohol, gambling, and the like. I am a liar."

The use of any drugs is likely to make ANYTHING worse. You dont say if you are dx bipolar but i'm assuming you are as you've posted here. any drugs or alcohol will destabilise you very quickly or just stop the meds from working in the first place. if it's as big a deal as it seems to be, ask your dr to get you in to some form of detox programme. Until you are clean of everything, you wont be stabilised.

"My grandfather just had a stroke. He was like the dad I never had. I have gone to see him in the hospital a few times, but I feel like I don't care and that absolutely kills me."
I'm really sorry about your granddad/. that's a lot of stress to add to your already chaotic life. I do hope he's going to be ok. Perhaps the feeling of not caring is just your way of coping. it's failry common.