Is it normal to want to believe a lie even when you know it's a lie ?

So my girlfriend is 32 weeks pregnant. We were on a 3 week timeout. I've been faithful to her even through the issues that led to us separating. However, when she and I reunited we had unprotected sex. To days later I started to have male signs and symptoms of STD.....need I say more? Sure enough test results rendered gonorrhea. She denied being with anyone of course but I know it has to have come from her ONLY!!!!!!!!! You can just hear the guilt although she's won't admit what she's done.