Quick question re splitting bills and borrowing/lending money

[y7anect001 at sneakemail.com]

I've gotten reasonably familiar with gnucash and understand split transactions (at least as far as salaries).  I'm not sure how to deal with expenses shared with my fiancee, however...

At first I thought it'd be pretty straightforward -- I figured I'd create an entry for her under Liabilities, treating our situation like a short-term loan, and just throw everything related in there.  Things are seeming more complicated though, and I'm  not sure how to handle them.

Any suggestions will be a huge help.  Consider the following cases:

1) My fiancee writes me a cheque and I cash it for her.  This seems fairly straightforward.  I set up two transfers, one to and one from her account.

2) My fiancee and I have dinner, and it goes on her credit card.  I expect to pay half.  Here's my first stumbling block -- how do I treat this?

3) My fiancee and I have dinner, and it goes on my credit card.  She'll pay half later.  I'm not sure how to handle this one either.

4) Similarly, I'm unsure how to handle a case where my fiancee or I pay 100% of a bill for the other, with the expectation that the money will be paid back entirely.

5) Finally:  We go out for lunch, spending $z, and both pay $x and $y dollars respectively ($x + $y = $z; $x != $y).  How should this be treated?

My apologies if this has been covered elsewhere,

Many thanks,

Cael