I doubt he'll change and I'll tell you why:

There's no time for him to change. Only three days have gone by and he's been abusive for years.

There's also no reason to believe he's sincere. More like he's in shock and just saying whatever to get you back. I doubt he's really thought about it or even knows the details of what he needs to do to change.

If you take him back, the message he will receive is that you have no boundaries and that there are literally no deal-breakers in this relationship. The threat of you leaving him was your only leverage and you've already played that card. Now you have no leverage. If anything, his next "episode" will probably be even worse.