Girlfriend is sponsor of ex--can I be held liable?

My girlfriend recently revealed to me that she's the sponsor of her Canadian ex-husband. Aside from my confusion as to why he won't get dual citizenship when he's been here for years, I started wondering...

If, in the future, we should decide to live together or get married, could I somehow become liable for her obligations as a sponsor through marriage or cohabitation or some other association?

If not, I guess it's her problem and she should just encourage him to become a citizen (or have him removed for something stupid he's done).

If so, are there things I could do to isolate myself and my assets to protect them from this liability?

Maybe I'm worrying too much about it, but obviously I don't want to be paying for someone else's mistakes that I had no hand in making.

Thanks!