Perfectly normal I'd say, especially after a really long relationship like yours - 24 years of memories can't be filed away in just 2.5 years and probably never will be.
Back in the early 80s I was married - not to a BPD - and although the marriage only lasted a few years due to various reasons I still today think of her family, who were lovely people, and loved me while I was married to her. I still get the odd email off her and we're on good terms.
She had two beautiful nieces aged 5 and 9 and they really took to me - took them about 5 seconds to realise I was a soft touch and the younger one could wrap me round her little finger

. I would have loved to have had two kids just like them if our marriage had worked out.
So 40+ years later, they're both married with their own kids and I still think of them and in my mind they'll always be those two adorable kids getting into mischief. Very happy days that will never leave me. If you truly loved people, their memory will always be with you so just enjoy those thoughts when they come.