Nobody is 100% at fault, in a relationship, both are responsible
for any problem that happens, just that one may be more are fault
than the other, the fault will not lie solely on one person.
As for changing yourself for your partner, it depends on whether
the changes are good for you, and if it is reasonable. You will be
willing to change for someone you love, but know ur limit and use
ur brain, see the reason to change.
People will always change over time, this is life. Whether a person
who walks away from the r/s need to change or not depends on
whether the person sees his/her mistake or any need for
change...