The other day I had a date, which went very well, and unexpectedly I ended up inviting her back to my place afterwards. I really like this girl, and would like to ask her out again sometime. You know, before you ring her up and spill all you have to say about your ritualistic nighttime hobby, you might want to reexamine her reaction. Semen might not have been the obvious deduction. Or even if she knew right away that it was semen, she may have merely been disgusted by the fact that the sheets were dirty.
People are usually cool about stinking away in their own filth.
The problems sprout when a person is asked to be a part of a stranger's filth. These are simple suggestions, really. Use lighter bed linen. Change your sheets before a date. Don't invite a date to your house when you know it's dirty.