Where did she move on to?

My ex said he moved on "to heal," then he relapsed and got his 4th DUI. Prior to that fiasco, he texted me goodbye and told me I was the most precious woman he had ever known and I would always be "the one." I asked him why he had to leave then but I think his girlfriend told him he couldn't talk to me anymore. 🤣 I am beginning to think relationships are not meant to last forever. But why?