If you can afford it...
...go out and buy a cheap all-in-one second stereo system. Get one from a second-hand store or whatever.
Set it up nearby your recording setup and you can monitor using the second hifi system. OK, not as good as fancy expensive monitors, but a damned site better than using headphones. Even turned down so not to annoy the neighbours you'll still get better mixing results.
When the girl friend isn't around you can check the results you're getting on the good hifi system.