What do I and where do I go if husband wants to file for a divorce and I don't want to sign because he threatened to take everything?

I had a boyfriend before my husband and I got married. He's accusing me of still having an affair, which is not the case at all. He has tabs on my whereabouts all the time (friends watching me, neighbors and so forth). My husband and I got a house together. He is threatening to take everything including full custody of our grandson. He can't even take care of himself. He is leaving me with all the bills we owe together. He threatened if I don't sign, he will have me pay him spouse support, and he is verbally abusing me, calling me all types of names and so forth.