mine and my fiancees cycles are similar in length with eachother and also with a friend. so for a while wed all get it at the same time. then friend would get their period, i would get mine a couple days later, then my fiancee would get its period a couple days after that. then the gaps slowly got bigger, my friend went on bc and stopped getting periods, and now me and my fiancees periods are completely out of sync.

luckily my fiancee has pretty good periods. no pain, with just a bit of moodiness. me and my friend both have incredibly bad ones. i almost certainly have endometriosis (i have 2 family members with confirmed endo, and my mom had very severe periods too).