Ex wants 50/50 custody

I fell pregnant to a brief fling. My baby is 5 weeks. I was in 2 minds of telling the dad who is not on birth cert. but silly me told him, but he started being controlling so i backtracked and said i am not sure if its yrs or my exes.
I dont want him involved. he also told me he is seeing different women etc, but wants 50/50 custody
I dont want this for my son. I should have went with my gut instinct and not told him.

Now i feel i should move interstate or run with my child.
I cant sleep, eat etc... feel so ill
i told him my ex did a paternity test and i will know results next week, because i dont want him around. he is a control freak. i hadnt seen him in a year and wanted to do the right thing, but the right thing is for me to bring up my own child with loving support he gets from my family.

How stupid was i to think he may have changed?

what do i do, ? my ex is not having a test and i need to get this person out of my life.
?
what if he wants a paternity test?