Spouse, ex partner or even someone you dated causally.
Mine were:
Long distance, London and Chicago. Too difficult for us to have any normal kind of relationship.
A break whilst I went travelling at 22, met someone amazing, had a summer fling. Ex wanted to get back together (he knew everything) but I couldn’t be with someone when I knew it was possible to love someone more.
My first boyfriend I realised he could never want/love me like I did him.