What's the difference between 「〜とつきあう」 and 「〜につきあう」?

Question

I understand that つきあう means "to hang out with, to date, to keep company…". I've seen it used both with と and with に, but I haven't been able to figure out when to use which. So for example, what's the difference in meaning between

彼とつきあう and
彼につきあう？

Answer 1

There is an important difference in nuance and often even in meaning.

Nuance:

(Someone) とつきあう = "to hang out with someone willingly"

(Someone) につきあう = "to hang out with someone unwillingly" because you feel obliged to do so.

Depending on context, 「(Someone) とつきあう」 means "to date someone" and when it means this, the phrase cannot be replaced with「(Someone) につきあう」. That is unless you are dating that person unwillingly.