Drug Abuser the father, stay or go?

Hello all. Sorry for the long post, but I'm thinking I need some outside advice. I'm newly pregnant (5w6d), and the father is an ex of mine I got back together with because I thought he had cleaned up.
In the past he fed me tons of lies, used every drug under the sun (I don't use any, barely even drink) constantly messaged other women, slept with other women, etc. I, for some reason would take him back because I loved him, and hoped he would change.
We ended up seeing each other again and now here we are, pregnant and on the outs because he never actually stopped doing drugs, never even attempted. Just hid it better.
I don't want my child to be in such an environment, now, later, ever. This morning the SO actually told me drugs are fun, they bring him joy and they're the only thing that does.
Should I stay and try to get him help? Or should I leave once and for all because it's obvious things will not change?