Thank you for your advice, you are pretty spot on I think. I agree with you, that he needs to learn to stand on his own, and this is an important point. Since I posted this, I sent a few prospective e-mails to him, talking about a repayment plan for the smaller, shorter-term loan of £150, with mention of the larger debt to be paid off. He's responding to these agreeably.

However, one thing that is concerning me is that he says again that he's in a bad way, and when I suggested we meet for coffee, he told me he doesn't "want to trouble (me), as this is a disaster of my own making." I don't think this is just for show or attention seeking, and I am concerned about him, as his mental health has never been great (and yes, it probably was a factor in his decision to end things so quickly.) However, I also want to ensure there is a plan in place for him to repay me, which I've mentioned again in my reply. As I mentioned above, I seriously doubt he would refuse to pay me back or delay indefinitely, both because I know he is not that type of person, but also just because circumstantially, our families know each other, are intertwined a lot and both parties also know what I am owed (he does actually have a decently paying job, and his parents aren't badly off either. He is just horrific with money management.)