I had a friend who, despite a four year age difference (he's younger, we're both males), was one of my closest friends when I was at boarding school. We kept in close contact when I left to go to uni and I was a regular visitor at his parents' home.
When my Mum was diagnosed with cancer he didn't really know how to react - fair enough, he was 16 and had no experience of it. When I went back to my home country to see out her final few months he didn't reply once to any of my emails or letters. He definitely got them, because his parents wrote after my mum died.
When I came back to the UK he was starting uni and we communicated regularly, but it was always me calling, always me suggesting times/places to meet up, and always him not committing because he was holding out for a better offer. When we were 27 and 31 he got himself into financial trouble - he and the friend-of-a-friend he'd bought a house with had bought half of DFS on interest free credit and when the 0% offer ended and went up to 34% he couldn't come up with his half. Not knowing he was already drowing in five figure debts I lent him £4k "for a few months".
Three years later, while I was away on a course, he rang my home number. By my reckoning it was about the third time in the 12 years since he'd left school that he had initiated contact with me, and it was about then that I realised just how once sided everything had been, because it was so unexpected. My assumption, of course, was that he needed something from me. He didn't leave a message, didn't call my mobile, but instead emailed me at work the next day so he would have got my out of office reply saying that I was away for the week. I got the message a few days later and emailed straight back. That evening I also called his mobile and left a message.
I am still waiting for him to return those messages more than 15 years later, and I've given up on ever seeing my money again.