What is the most correct reason for couples to break up?

I love you, but I can't give you the best life, so I let you go. At first glance, this reason is, um, very touching. Coupled with the tear-jerking performance, people can burst into tears in minutes. In fact, the heroine cried after hearing it. However, the point is that in less than a week, she saw her ex-boyfriend smiling with a beautiful girl in his arms, and she was completely awake in an instant. What I love you and do for you is just to break up with you to make room for the girl she likes. Not loving is not loving. Why cheat?