Dean would desperately work to save Sam, and all thoughts of the case would be thrown out if he saw his little brother in such a bad position. He’d try and get Bowman to help him, his little brother is hurt, what if he dies…

Bowman, on the other hand, would be quite willing to help (which is why he shoved Sam away from the spider in the first place), but if he’s got a very intense and possibly accusing Dean on his case he might get flustered. He knows some of the right plants to help with a bite, but in the end his skill isn’t enough to do much healing so Sam would have to wait it out. At this stage, there’s no way Bowman could trust Dean enough to bring him to the village.

Remember Bothering Bowman, when Dean and Bowman argued in actual circles? It’s just how they make friends when there’s no Sam providing mediation.