I think that Brian was just taking care of some long over due family business. I know using the term family here is odd but he had to show Michael that they were better friends/brothers and wouldn't possibly be good lovers or partners for each other.
I dislike this whole episode because it showcases Michael's immaturity and forces both Ben and Brian to deal with this the way you would a child, and puts Brian in a place where his integrity in regards to the rules he has with Justin is question. To me this goes beyond those rules because this is Brian dealing with his Brother and trying to snap him out of his shit the only way he knows how.
This was a Brian cliff push with a bit of a scared straight program mixed in. You can see he is heartbroken over this. The kiss looked tortured and mechanical with no real emotion behind it. I think that Michael even though he lusted and longed for Brian he was too much of a pussy to really go for it, or maybe he didn't even want it he just likes the idea of it. To me that's what Brian's "I know your secret identity" line was all about.
I felt so bad for Ben in this episode, having Michael interrogate him over what it was like to fuck Brian was pathetic, not only because it wasn't his business but because it would be tough for Ben not knowing which way the jealously fell. This episode is when I washed my hands of Michael.
Honestly how anyone could think that Michael was this awesome caring person after seeing how he treated both Brian and Ben like puppets makes me shake my head.