Email

A family member's girlfriend had been accessing my email account for a few months before I became aware of it. They even admitted to it. I realise that it's my word against theirs but do I have any legal recourse?

Depending upon how it was used, and what proof you have, you may very well have a case against her for identity theft. Much will depend upon the laws in the area where you live.

rubbercrutches is right, but you'll need proof.

If there's none, then your best bet is to change your password and chalk it up to experience.