@jespah,
Well jespah, that was quite an answer. Thank you, it did so much good to me although it was, well, a bit brutal - but so true, and I am not being sarcastic, believe me. I didn't know the meaning of ghosting, so I went looking, read some articles etc. I got a shock, this was exactly what had happened to me. I didn't know this was a relatively common way of dealing with unwanted lovers. There was nothing I could have done, it had nothing to do with me, and it feels so much better now, thanks to you and your quick and simple post.
(Still, the mystery remains. Why bother with a card and "my love always" instead of simply vanishing? So I wouldn't suffer as much and wouldn't feel bad?
Well, it was the opposite!)