I absolutely agree with everything that darlaisabelle says.
I had the same reaction as you when I first watched S2, miss_cephalopod, but I think D, is right. There was a lot of self preservation (on Brian's part) and miscommunication going on. Brian was not shown love by his parents, so since leaving home I think his default position is not to place himself in a vulnerable position. The jealousy he felt over Justin and Michael's collaboration/feelings of rejection has reminded him that he does not want to be in a vulnerable position and so he has stepped back.
also neither of them communicated well. Brian didn't explain in advance that he couldn't go snowboarding and why. Justin didn't admit that he really did want his birthday celebrated (that was the lowest Brian moment).