Dean And Ruby

Here's something I found strange in season 3 and season 4 of Supernatural concerning Dean and Ruby. In season 3, one minute Dean was listening to her and letting her help them and then the next he hated and mistrusted her. So what the hell was going on with that. Then in season 4, Dean finds out that Sam has been hanging out with Ruby and he tries to kill her. Then he finds out Ruby saved Sam's life while he was in hell and thanks her and goes to protect her from Uriel. What the hell was that about? Then all of a sudden Dean doesn't like her or trust her again. It's funny to me that Dean found out that Sam was talking to Ruby again and he didn't do anything about it. He didn't even talk to Sam about it or find out why Sam was in contact with Ruby. Then in "Death Takes A Holiday", Sam told Dean that Ruby was following him, but Dean didn't seem all that worried about her and he just didn't want her help. I thought to myself the whole time that Sam was lying to Dean, why didn't Dean try to find out what Sam was lying about, instead of acting like a two year old about it, why didn't Dean confront Sam about it? Why did Dean wait so long and then found out what Sam was doing and just threw Sam in the panic room without even finding out what Sam was really doing.
Also what was the deal with Dean. If he knew Sam was lying to him, then how did Sam sneak out to see Ruby and drink demon blood all the time. What was Dean doing? Did Sam slip out of the motel rooms they were in and Dean was dead to the world and never heard Sam leave. Or did Sam say he was going out to the store or something. I don't understand any of that at all.
Another thing is, people think Dean owes Sam the biggest I told you so, ever. What the hell? What did Dean tell Sam? I never once heard Dean telling Sam not to go near Ruby or that she was just an evil bitch that was using him. I never heard Dean tell Sam anything. Or was that more stuff that we were just supposed to assume because all of Sam's storyline was off-screen. Maybe after Dean told Ruby thanks for saving Sam and then Dean protecting her, maybe Sam thought Dean was okay with her. Even though Sam lied to Dean, what the hell was Dean doing the entire season? I just don't get it.
What was the deal with Dean's whole attitude towards Ruby? One minute he was okay with her and then the next he wasn't. Were the angels or demons doing something to Dean? I wonder about that because I just think Dean's whole attitude towards Sam and Ruby was weird and that Dean never did anything until it was too late. If Dean thought that Ruby was so evil, why didn't he try to kill her before he found out what Sam was doing with her?
It's not a popular thought about Dean's attitude towards Ruby, but I think a part of Dean was jealous of Ruby. That Ruby became a part of Sam's life and that Sam started to trust her. I think Dean was pissed off about that and it wasn't just the fact that Ruby was a demon. I think Dean was pissed that someone else could take his place in Sam's life, even though, Ruby didn't take Dean's place, even though Dean might have thought that.