Do I talk to a lawyer or what do I do?

I have two kids-same dad (newborn and almost 2.) He also has an 11 year old of his own. Long story short he has a drinking problem and has since ive known him. He has had maybe 2-3 short short periods of sobriety but it never lasts. He doesntbring his 11 year old around, but when he has been around he put his hands around my one year olds neck and try’s hurting him when he thinks we’re not looking. I told him it needs to stop and he accuses me of hating his son and being terrible to him. He disrespects me right in front of his dad and he doesn’t do anything about it. BUT HE SPANKS AND YELLS CONSTANTLY AT MY ONE YEAR OLD. I told him he better never touch him again. He pinched his face so hard to “teach him a lesson” that it left a bruise. Well I just left him, for good and I’m nervous about him ever getting the kids alone. Do I contact a lawyer or do I wait and see if he will tape me to court? I don’t think he will because he already pays 409 in child support and is on probation.