Lets call the friend Jeremy.

Jeremy and I bought tickets to a concert in another city, fairly far away (requires flights/hotels/etc). The tickets were about $200 and non refundable. We agreed to go to the concert together and paid for our tickets seperately. The next day Jeremy decided he doesn't want to go to the concert the original city we decided on, rather another city that they like more and would rather visit (also just as far away). We again bought tickets separately to the same event, now in a different city. I am now asking them to help cover half the cost of the tickets to the original city since they decided to change their mind. I am not that hellbent on the money, rather the principle of sticking to your word - and if you change your mind you face the consequences

AITAH for asking my friend to help cover half the cost on the event since they changed their mind?