When changes are not welcome

What makes a partner change? Is it because he's bored with his other half or, is it because the other half has changed him?

I think my partner has changed a lot. Sometimes, I feel I don't know him anymore. Like a stranger. Like someone whom I've not been living with for almost 7 years.

Or is it me who has changed or have too high an expectation???

I sometimes wish we were like we were six or seven years ago, plus A and Sy, of course.