Originally Posted by Daniel_

If you have the panties, you could always go CSI on them.

You could use a UV lamp and look for the characteristic fluorescence of semen. Given the right (relatively simple) reagents you could even test for semen. In fact, if you keep them before they're washed, you could spend a couple of hundred dollars and have a DNA test done on them to find out who donated the semen.

All of these are TECHNICALLY possible, but not necessarily sensible.

The best option is to talk to your wife and explain that you are tearing yourself apart with worry over all these pieces.

If she wants to fix things, she may explain, and if she wants to end it all, she'll tell you to go to hell and pack a bag (I expect).