Opinions wanted

Please read the scenario first.

Ken: Do you want to go to this concert next month? It's a $5 cover charge. Heath's favorite band is playing.

Heath, Kirsten, Jim, Cain, Donald: Yeah,  sure.

~3 days before the concert~

Ken: I don't think I can afford to go.

Group nods.

The group then goes to the concert without Ken. Heath wins a shirt and CD from the band. Jim posts about the win,  along with a group pic of them at the show. Outside,  after the concert,  Ken shows up,  screaming.

Ken: WHY DIDN'T YOU TELL ME THERE WAS A CONCERT? I CAN'T BELIEVE YOU GUYS ARE SO RUDE!!! I'D HAVE GONE IF I KNEW YOU WERE GOING. I'M SO DONE WITH YOU JERKS.

Jim: Sorry. Thought you said you couldn't afford to go.

Ken: That is no excuse. You and Heath should have called,  texted,  emailed,  tweeted, and Facebook posted to me so I'd know about the concert. Obviously Heath doesn't want me as a friend anymore. I'm not good enough. Cain or Donald can be his friend now. I'm so done. You are horrible people.

Heath: But you said you couldn't afford to go.

Ken: I said I didn't THINK I'd be able to afford it. Then I sold some stuff on eBay and made an extra few bucks.

Jim: But you didn't tell any of us that.

Ken: THAT ISN'T THE POINT!  YOU SHOULD HAVE MADE SURE I KNEW ABOUT THE CONCERT AND TOLD ME YOU GUYS WERE GOING!  Jim, you should have sent up a bat signal at the very least,  since you don't have my number.  I can't believe I have to explain that. My feelings are so hurt. Especially by Heath. We're supposed to be best friends. How could you treat me this way?

Jim: Wait,  wait,  wait... We were supposed to check in to see if you were still broke and rub it in your face that the rest of us were going? It's Heath's favorite band,  not yours. We figured if you couldn't afford it,  that was the end of the conversation.

Ken: I texted Heath 3 days before the concert. He never got back to me as to if he was going. He didn't reply that day at all. That's why I wasn't going to spend the money to go. The money I didn't have. But then stuff sold on ebay. But Heath should have texted back.

Donald: Heath and Kirsten were at her Aunt's funeral that day. You know that. They didn't have their phones on.

Ken: That has nothing to do with anything! 

Heath: I saw your message about being broke. That's why I didn't reply to the text the next 2 days. I figured it meant you had changed your mind about going. Last time I asked if you were going to something you couldn't afford, you unfriended me and we didn't speak for a year. I didn't know what to text because I worried anything I said would cause you to leave again. With the funeral and all,  I couldn't take losing you too.

Ken: I should have been communicated with!  You all left me out on purpose. You're horrible people. And Heath doesn't even own a poster of that band! If Kirsten really loves him,  she'd have bought him a poster. No poster,  no relationship!

Jim: Yeahhhh... That's not how it works.

Kirsten breaks down in tears,  sobbing that she's a horrible girlfriend who bought flowers for her dead aunt and paid rent instead of buying an autographed poster for Heath. No one can console her,  no matter how hard they try.

Ken then calls Heath's brother Ben. Ben agrees that Kirsten should have bought a poster. Paying for Heath's college tuition,  their apartment,  and staying in a committed relationship for ten years is NOTHING without a band poster on the wall. And no,  buying the imported CD with limited edition cover art and two previously unreleased songs DOES NOT COUNT. Savages.

Donald flips out on Ken for attacking Kirsten, who is his sister. Cain and Kirsten have to hold Donald back, because he's ready to give Ken the end-all be-all of a beat down. Death threats are shouted. Strangers slink away.

Hours later,  Jim is still trying to figure things out. Heath has apologized to Ken because Ben threatened to disown Heath if Heath didn't make it right with Ken. But Heath is now hurt because of Ken. And Kirsten has sunk into a deep depression. Ben says that no one else saw Ken's side of the story.

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Okay, so how did the group wrong Ken?
How can Ken's side be better explained so the group can understand and not make the same mistake?

Opinions needed!