I think we attach to anyone we work or are with for any period of time. We are in the same situation, working together on some project (of our own or of a group nature).

Attachment is a natural bond, not just for parent/child or whatever other "problem" we are working on but all animals attach/imprint/whatever. Mothers attach to babies with the help of oxytocin, partners attach with sex hormones, etc.

There has to be a bond of some sort, a "cable" to get the electrons going both ways, your printer is an attachment to your computer (wireless nowadays :-) a conversation is an attachment, it's learning and interacting. The strength of any attachment is merely our history, background, inclination, experience, nature/nuture, etc.

We invest in those we are attached to and change means we have to withdraw that attachment and reinvest in the next. How strong we've made the attachment, how much glue we've decided to use on our side, and how well we have learned to handle changes, those things go into how well we navigate life.