how does one differenciate clearly between pure sentimentality and any true feelings of 'love'?

i just broke up with my girlfriend, and she can't accept it. she's been saying how she thinks we can still work out etc. etc.

I keep having second thoughts now, but i don't want to go back just because of pure sentimentality.

well, you can't.

It will always be a mixture.
just do whatever you feel best with.

good luck