Sounds like the D&D group is derailing quite a bit. xD I can understand characters doing shenanigans, but I'd say it kinda sucks when people won't cooperate.

I myself would have probably just tried to leave the rogue behind. Like "So you just want to do your own thing? Okay, goodbye. We need people that know of teamwork for this quest." And then the thief would probably just die somewhere being jumped like you or caught or something. :P