J.N.
Dear G.,
Bless you for being quick to catch on to what may be going on with your Ex. Go with your gut, if you think for any reason that he might harm your child you have to protect him. A mother is the best and most important advocate for her child. Chances are that if he hit you then he would be capable of hitting or shaking your baby. The disorientation and unusual behavior sounds like your baby my have been a victim of shaking.
This is very serious and you are going to have to stick to your guns and go fight to protect your son. I think in this situation if the visits are court mandated then you need to be sure they are court supervised at the very least until the sherif's investigation is complete. If the sherif proves that he is abusive I personally feel his visits should be terminated. A 5 month old has no way of protecting himself from an abusive parent.
For more help I suggest you contact CAPA:
Child Abuse Prevention Association - CAPA
503 E. 23rd Street
Independence, M0 64055
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Fax: ###-###-####
As for "not being able to handle much more" I'm afraid that you have to step up and just do it. Being a single mother at 18 is not for the faint of heart. Not only are your still evolving into the young woman you will be you are having an crash course in parenting at the same time. I imagine this occasionally feels like a trial by fire for you. You have to remember the best steel is forged in fire. It makes is stronger, able to with stand incredible force and pressure. So, be strong for your son and proud of yourself.
God Bless,
J. N.