He's practically searching for any reason to doubt her

No,i think he know in his Heart,that he can never be the one and truely love of her life:)

I thinks he really wants to, but he can't...

Bye Bye Louis! you won't be missed :)

He thinks she's lying about anything in every episode since his return in 4x19.

4x19 - "You're going to kiss him?" "Serena said you've been seeing him for months."

4x20 - He didn't trust she was completely over Chuck.

4x21 - "I know you saw Chuck. Twice."

4x22 - That little look he gave them when they were talking about their great love.

5x01 - That little look he gave Dan and Blair at the loft. He is full of insecurities.

5x02 - I don't remember, but there has to be SOMETHING.

5x03 - he wasn't really in this episode until the end.

5x04 - Do I even have to explain for this episode!?

Louis is more jealous than Chuck.

It looks like he's going to find out that Blair had a paternity test done so definitely not.

He secretly wants to leave her I think and he better because we all want and secretly believe the baby is chucks and chair is meant to be so it's a win win situation chair forever. Chuck and Blair, Blair and chuck

i can tell just by his look at the end of the episode

I think If blair really marrying him, they both will have one miserable marriage! he's too insecure, I don't think he will ever trust her