Mybump...I'm so sorry about your dog. Can you take him to the vet to see if he's ok?
As for your X, DO NOT let him into your home again. If he pounds on the door at 2 a.m. again, call the police. Change your phone number, change your email and cut all contact. He is clearly dangerous and this is no reflection on you.
When you met the man two years ago, there wasn't a neon sign above his head that said "Psycho When Blotto". You couldn't have known.
Keep yourself safe.