Will he change? He is in jail?

Okay. I have been with this guy for 3 years off and on…
While we was split up he started smoking Crystal meth.
I recently got pregnant and he is trying to quit (which he just went cold turkey)…
he got very angry and possessive and didn’t want to loose me and started threatening me when I would talk about leaving him or going somewhere with friends without him.
When we first got together he had not been on it and was great and when he started it he was still the same man but of course some what different.
He has never acted like this but then again he has never had an addiction like this before.
I know it has alot to do with the meth but he is now in jail for agg. assault and he says it will all change and he will be a different man.

I broke it off with him because I think that he is going to have to do this on his own and I cannot risk loosing our daughter..

I just want to know if you think someone who wants to change and has to do it the way i am having him do it and with my support will change when he gets out of jail…?

please do not yell at me and say i am crazy…he was never this bad….i do love him and if he can change i want to make it work