my heart broke just a bit last night....kid related

So, I posted yesterday about my oldest son, Colton, stating that he really is a good kid. He really is, but he broke a bit of my heart last night, as well as his little brother's.
I know he is a typical teenager and most times they don't think before they say something (or do something), and I know that alot of that will get better as they mature, but what he did/said last night just tore at my heartstrings severely.
Colby is a pre-teen, 11 yrs. old and will be 12 in two months. A very sensitive and awkward age, IMO. He started middle school this year, so he's really exploring lots of new things/interests. Girls, class subjects, etc.
Colton (the oldest) has been in the school band program for 4 years now and is active in the drumline. He has been self-taught various percussion instruments, as well as the guitar.
Colby decided to join the middleschool band program and was quite pleased that he was accepted in to the percussion group, following his older brother's footsteps.
Last night, Colton informed me that he would be having drumline practice two nights per week, as the drumline decided, as a group, that they wanted to participate in a few of the regional competitions later this spring. OK. Fine, that is great.
He then calls me in to his room, wanting to show me something. He gave no clue as to what he wanted me to see, but Colby was sitting next to me and jumped up to go with me.
Colton rudely told him that he had not been invited to see what he wanted to show me and closed his bedroom door in Colby's face.
Colton proceeds to pull up a YouTube video on the wii wi-fi connection and tells me that this is the music that the drumline is going to perform at their upcoming competitions.
I asked Colton why could he not have let Colby come into see it with me and he just very nonchalantly stated that if he had wanted Colby in there to see, he would have invited him to see it.
Colton is, and always has been, the type of kid to not let things bother him, verbally or otherwise. He just sloughs it off and goes on about his business. I've seen it a few times with his friends. He quickly lets things go. He has ALWAYS been a compassionate child, much to my amazement at times. He's very laid back and makes friends very easily. He doesn't have any one girlfriend, but has literally dozens of girl friends, in real life and online.
So, I was quite surprised by his response when I asked him why he was being so rude to his younger brother.
His response?
"Mom, I don't let things get to me or bother me, so Colby shouldn't either."
My jaw dropped. I could not believe these words and actions coming from Colton. I was dumbstruck. I was numb.
I tried to explain to him that he was not the only person whose feelings should be considered, but he looked at me like I was a martian, totally not getting it.
I informed him that he was not the only person in this house whose feelings needed to be considered, and he actually argued back and stated that he knows that, but still felt the same way.
I could see that he was not going to get it anytime during this conversation, so I told him to just stay in his room the rest of the evening, took the wii out, and told him to do his homework.
Left the room to find Colby, whose feeling had indeed been hurt tremendously. Colby looks up to Colton...this was devastating to him.
I mean, what do I say? I honestly had no words to repair the damage that had been done.
All I could do was hold him and tell him that we all say/do things that we don't always take in to consideration of others' feelings and that Colton was just being a butt. He was soooo hurt.
I was hurt. I was hurt because I am trying to get my kids raised with respecting others, and I felt that at 15, Colton should be more wary of what he is saying to his siblings.
I was hurting for Colby. My heart is heavy today for this child who only shows admiration for his older brother and is trying to "find" himself at this awkward age, but yet does not know any other way to do just that, except perhaps emulate his older brother.
I know that this is probably just one of the many conflicts that they will have, but it sure makes for a sucky feeling, and I am just feeling out of sorts over it.