OP, fucking wake up. You're doing the wash and you want to know why your wife might be fucking around? Are you whipped or what? Jesus H. Christ, grow a pair.

Scrape a small amount of the substance into a clean container or baggie and surf the net for a lab that does specimen analysis. Probably cost you about $50. It will be the best money you ever spent. If it comes up clean you bought piece of mind. If it is semen, you now know the absolute truth, before you confront her. Because if you confront her with only a suspicious, she will make you feel like a piece of shit for a very long time. Trust me spend the money and GROW SOME BALLS MUTHERF**KER!!! LOL