Thickening of the ejaculatory fluid is most commonly secondary to dehydration. The first step is to try and increase water intake. After a few days, the fluid should become thinner and the "gelatinous" material will disappear.
If drinking water does not help, I would suggest he see a urologist for further evaluation and treatment. If he has any penile discharge, burning with urination, fever, if the symptoms persist, or back pain develops, please see your doctor immediately.
I hope you find this information helpful.
If the individual had pain or discomfort or if he was embarassed by the thickening of the ejaculate, it may decrease his sex drive. Otherwise, it should not directly affect sex drive.