If you get more than a little grossed out when these things happen while giving your partner a hand job, don't worry — you're definitely not alone.
Another suggestion, you can try using some lubricants for better stimulation, it can be sometimes more pleasurable if you feel the wetness etc.
The Pre-Cum Dries Up Remember back in grade school when you'd get glue on your hands, so you'd rub them together until it dried up? And then, if things don't get wet enough in time, it'll start to roll up into tiny pieces that either stick to your hands or your partner's penis or it falls off onto the sheets.
One reason can be that it is because of the fact that you are used to self-stimulation during masturbation.