I'm sorry this happened. I am not a proponent of dog parks. We can't expect all dogs to get along...some get along just fine, while others don't. For me not worth the risk.
Best advice, carry on, watch how you react around your pup he will pick up on your emotions. If he must play with other dogs let it be with a trusted dog that you are comfortable with.
Poor little guy....but he's probably tougher than you think. Build his confidence, focus on one on one time