How do you maintain that "in love" feeling long term?

Hi ladies my SO of five years and I very recently split up. He told me he just didn't have the same feelings anymore and was no longer in love with me. I too had been feeling the same way for quite some time so it's not the biggest shocker. He said he loved me but now in a friendship type way. We spoke about it and I told him ive been feeling the same but I wasn't sure if it was normal after being with each other for so long. He was my first relationship but I'm not his. I guess my question is does this happen in long term relationships? How do you make sure you keep that "in love feeling" with your spouse/SO? Especially after so many years?