I feel like buying and drinking alcohol in front of him could be good natured. Especially between dudes. (Speaking as a dude.) Like, the whole "iron sharpens iron: thing. Kaelen trusting him to not give in, helping Vitek strengthen his self control. Something Gregor would openly encourage him do to. 

FYI, Gregor sees such potential in both of them, and knows they can hone one another. He believes in their sacred and wild strength. He wants to guide them to control, but wants them to be able to unleash their full power when necessary.

Just a lil above table knowledge.