Is it true that once you loved someone you will never stop loving them?

I feel like this is so true and it frustrates me so much..I had a very bad past relationship that lasted on and off for 3 years. He was a liar, deceiver, cheater, and i spent more time crying than smiling with him. I was a fool for letting it drag on for so long but I learned to finally say no to him. He would leave me so many times and the last time he did, i promised myself i wouldn't chase after him and i didn't. He ended up crawling back to me, begging me to take him back and i said no. I now have a new relationship and i couldn't be any happier! This is the man of m dreams, the complete opposite of my ex. However, from time to time i think of my ex and i always WANT to wish him the worst for everything he put me through but i just cant. WHY? Why do i think of him and still feel like i want the best for him. He texted me out of the blue on thanksgiving to wish me a good holiday and from there he kept saying how much he missed me and i DON'T want him back, but it hurts to just know that i gave him so many opportunities and he always ruined them, and now its too late..why does this happen and will i always love him even though i will never be with him again?