Does the milk supply decrease when I ONLY pump milk and I don't give my breast to my baby at all?
Babies are generally the best way to establish and maintain your milk supply and when you pump you are essentially tricking your body into thinking it is a baby. It is possible to maintain your supply if only pumping but it is important to regularly stimulate your breasts so they replenish what has been removed. Replicating baby's feeding schedule is a good way to do this. If someone else is feeding baby when you wouldbe nursing, pump at that time. Dont limit the pumping time, rather, let your body let the milk down and keep the pump going until the streams of milk slow down or stop.