Custody issue, please help

My husband and I are having marital problems, and will soon be working on getting divorced. I’ve asked him for a divorce multiple times but he’s always fought me about it and refused. I have a boyfriend now, and he (my husband) has been sleeping with someone we know.

My husbands mom lives four hours from us, we often let our son (3 years old) visit his grandma a week here and there.

About a two weeks ago she came and got our son last minute. My husband set it up, and I okayed it thinking it would be fine. My husband left a couple days ago to go get our son and bring him back home. He’s now texted me saying he’s staying at his moms and I’ll need a court order to see our son.

Were living at my parents as were renting from them. I have been a house wife so I have nothing. No license, no car, no job, no money.

How do I even begin to get my son back? I only want 50/50 custody, I don’t even want full custody.

We live in Texas near Austin.