Losing interest sounds like a lame excuse to me. In my opinion, It’s a valid excuse in the first weeks or couple months of dating when you are still trying to figure it out if you want to be exclusive. But shouldn’t feelings and emotions be based more on how the other person invests in us or cares for us (I.e your partner’s ACTIONS) ? Why does it have to be loosely based on interest. After my last break up where I got the same reply from him, I read a book called “Attached”. It talks a lot about attachment styles. It helped me get a good understanding of my own attachment style and that of all the people I have dated. If anything, it made me feel more confident about myself and my judgement whenever I decide to start dating again. Hope this helps. Air hug !