REF. Jane Yeah, Walt took the money over to Jesse and left it. He begged Jesse to get help with his drug addiction. He and Jane were both doing heroin. Then he went to this bar to drink and think. He told Skylar he was outing trying to find newborn pampers and the stores were all out! Too funny. In the bar he sat next to Jane's dad, which he had no idea. They struck up a conversation about their kids. Jane's dad was worried about Jane, because he had discovered she had relapsed and she had promised to go to rehab the next morning. Jane's dad told Walt to never give up on family. Walt had said his nephew was worrying him a lot. (He was referring to Jesse.)
So, Walt taking the advice to never give up on family went back to Jesse's apt. to try to talk him into rehab one more time. He sees them asleep through the window and goes him. So, he was there for a good reason. Actually, letting Jane die, was the thing that got Jesse motiviated enough to go to rehab.
What I never understood is why Jane's dad intentionally caused that mid air plane collision. It wasn't a mistake. You could see him watching the planes collide and he kept intructing them to do it. I never got that.