If you break it, you should buy it. That’s a pretty good rule to abide by, no matter what. 

If you’ve borrowed an item from a friend, and then it breaks while under your care, it would probably behoove you to offer to pay for it. This is a pretty basic tenet of life. You don’t want your friends to think that you’re cheaping out on them and sticking them with a bill that you caused. It’s not even always about the money. It’s about the gesture. You have to treat your friends with respect, or else why would you expect them to be friends with you? Relationships are built on trust, and if you can’t have that, you can’t have anything. That sense of trust eroded in this friendship, and they weren’t quite sure what to do in the aftermath. 

When you reach a certain age, it’s time to start taking responsibility. When you’re under a certain age, you can get away with some less-than-perfect behavior. It’s how you learn. If you don’t make mistakes, then you will never grow as a person. But once you hit a certain level of maturity, you should probably look in the mirror and realize that the choices you’re making aren’t always the best ones. Maybe it takes a certain canon event for you to truly realize it, or maybe it’s small things coming together over the course of time.