Help with prepositions..

Hi there, I have been studying English as a second language for quite some time now but I still get confused when it comes to using prepositions.

Please look at the following sentences and tell me the difference b/w them:

Her obsession with mirrors is unfathomable
Her obsession to mirrors is unfathomable.

Are both of those sentences correct? Or do they both portray a different visual image?

How about these two sentences:

The same thing happened with me on my first day at school.
The same thing happened to me on my first day at school.

Can to and with be used interchangeably?

Appreciate your time and help.