A while back, I went through a similar first time experience with my dog. I thought it was cute when she came to my rescue. My family was roughing it up on the floor, and my dog came running in from another room. She began pulling my wife and kids off me. It wasn't aggressive, but looking back now, it was a mistake. Lots of things could've gone wrong.
These dogs react to excitement. It's very easy for me to "ramp up" my dog.
My advice to you, would be to understand and respect what your dog is thinking. It's a natural response. Whether or not you can train a GSD to go against its natural instinct is another topic.
Don't set him up to "protect you" from other family members. You own a GSD, and with it comes some sacrifice. Wrestling in front of him, may be one of them.
If you need to wrestle with your boyfriend, put the dog outside. IMO, even a crate in the house, would raise his frustration level, because he'll still hear you, and want to get out.