I'd keep them separated for the most part and any interaction they have together should be supervised. Gsds can play rough, but there needs to be limits. Your pup/male seems to be bonding with your other dog, not you. You need to work with him and show that all good things come from you, play tug, use a flirt pole, fetch, OB etc... this will help build a bond. You can feed a portion of his food by hand while training him, this should help with the bond issues as well.