Summer is probably accurate
If Ethan didn't provide an adequate reason for their break up
-wasn't really in love
-too different in hobbies
-going to different colleges
-your grandpa scares me
then it's more than likely a bad reason
You don't just break up with someone and say "well I can't really tell you why, I'm just going to leave though"
But summer does have shitty taste in boys
remember when she was about to fuck the dude who was going to bully Morty?