Ex Wants to Get Back Together

I had dinner with my ex and saw him for the first time in four months. I genuinely had a very good time and he said the same.

We broke up four months ago. The feeling was sorta mutual but he initiated it. He has expressed to me that he wants to get back together.

I need advice. My heart and mind are at battle with one another. I know in my heart that I do want to be with him again, but I also know that things couldn’t have possibly changed enough in the past four months. I really do miss him. How should I go about this?

Update (based off of some of the comments already): we were together for five and a half years and we have never broken up before this time. On his side, we broke up because he felt like we were always arguing and he could never make me happy. On my side, I felt we should break up because he doesn’t have any ambition for a better job/career or better life than the one he was brought up in.