I'm new here but have been reading the boards for weeks now and a fan of the show.What I will say is this. Yes, Will clearly didn't try to change Janelle's mind. Normally he would have made every attempt to change her mind towards what he wanted but he made little or no effort to do so.
Why will always remain a matter of speculation. Janelle fans will believe it's because he "knew" Janelle outwitted her. Erika fans will think similar thoughts. Will fans will prefer to think that he did it for Boogie.
For whatever reason, Will appears to have given up. Maybe he was tired, felt as he said that you can only tell so many lies before people catch on, or something else. But he behaved decidedly unWill like.
I am of the opinion that he just plain gave up and decided to go.