What is one exciting romantic experience you hoped would last, but it didn’t and why did it fail?

Never been ambitious about getting into relationship,so can’t say

I had something like that toward the ending of last year. Have been talking to this girl well has friends for about a year then I decided to ask her out and she agreed. But two weeks to the relationship (weird right) I decided will stop cause I started losing interest and all. Before even asking her out I thought the relationship will last cause will understand each other