<human>: Could you distill the essence of the text into 1-3 sentences?

Okay...about 8 years ago, when I was quite stupid, my boyfriend at the time was very close with my family and mom (we were 19-20). She always said that she wished she could adopt him. He was a runner in college, and got injured. Long story short, he needed a way to stay in shape, and my mom ended up co-signing (I know...Looking back I am KICKING myself) for a loan (around $3K) for him to get this bike. 
Fast forward a few years...we break up (remained amicable), he moves away after we (he never actually finished/graduated) finish college and lo and behold, doesn't make payments on his loan. I have to call him every month, because my mom gets notices of non-payment. He buys himself a new car, gets a manager job at Abercrombie, yet still can't make a $20 payment each month. This goes on for a couple years, me calling him and telling him to pay his bill, and finally my mom just paid off the balance because if the loan defaulted, she would lose her business license. You guys, I feel so terrible that I put my mom in this position. I would pay her back but I'm a medical student and I just don't have that ability at this point in my life. What the heck can I do? I know legally there is nothing I can do--but I am so livid right now. I want to Tanya Harding his ass!!! Advice, please!!
<bot>: Ex-Boyfriend stopped paying loan my mom co-signed for. She just had to pay the balance. I'm real pissed.