I am a lesbian and have never been with a male. My girlfriend is bi and I'm worried that she cheated on me. Last week, my girlfriend "Vivian" said we couldn't have sex because she had a yeast infection that would take a few days to clear up. I came home early on Friday and some guy was sitting on our couch. I've never seen him before. Vivian was in the bathroom and she took a long time coming out. After she came out, the guy left and I said, "It's Friday we can have sex."

Vivian said she didn't want to, but I kissed her and rubbed her breasts. We took off her clothes and I started eating her. She tasted different. I said so but she said it was just because the medication had killed all her yeast. Then I started finger-fucking her and when she came, this big white squishy blob came out of her pussy. I was like "What the fuck is that?"

Vivian's face got all red and she said that it was probably just some of the anti-yeast medication that hadn't been absorbed. But I think it was man-cum.

How do I tell for sure?