Me (F 21) and my ex (M 21) trying again.. Need help

I apologise in advance for the length. We dated for 3 years (started when 16yr/old). We were best friends & super happy. We did long distance for 9 months (myself in Australia & he in America), he came back and we continued for 1 year. We broke up because we had grown in to different directions & had separate goals for life.

Fast forward 2 years and we meet up again. Somehow everything just seemed to fall in to place in regards to life goals. I had always wanted to travel/live in different countries and he never wanted to leave Aus again, now he wants to travel and experience the world too. I always wanted to move out and rent together, he wanted to wait and buy... now i want to save and buy too. Silly things like that.

The problem was, when we broke up... i took the stupid approach and got in to a rebound relationship as i was young and didn't know how to cope without my best friend anymore. This fucked him over so much and i feel incredibly terrible about this. We have been 'seeing' each other for almost 4 months and he isn't sure if he wants to make it official. We go to each others houses, see each others families... hang with each others friends etc.

Problem is, i asked if it was a 50/50 on the fence of staying and leaving and he said no, but is afraid of getting hurt again and feels terrible because he can't speed up his feelings (i don't expect him too, just wording). He doesn't want to commit unless he is 100% sure he can emotionally connect 'seriously' with me as he doesn't want to lead me on or hurt me more. His feelings are increasing over time, but with this comes an increasing amount of confusion and he isn't sure if he is on the same level as me, but it would hurt a lot of things ended.

He also said: I don't want to give the impression that I'm like considering stopping talking to you, but I also don't want to commit before everything is clear to me and then end up hurting you more.

When we started seeing each other again, we both decided complete honesty will be the best for us and communicated everything that we felt we needed to move past (in regards to breaking up/problems etc etc - not that we ever really had many) before anything else and it worked really well.... now its just this feelings/commitment thing.

We talk every day (both initiating) and see each other at least once a week, sometimes twice (both are very busy with work at the moment).

Questions: Has anyone else been through this? Did you stay? What was the end outcome? Do you think this is a matter of time and security within each other, or he just isn't ready to completely say goodbye to me? Do you think he will be able to commit in time?

tl;dr: Getting back with ex of 3 years after 2 years... he isn't sure if he can 100% commit after 4 months because he was so hurt last time.