It may be that he is a jerk who overreacted. Or it may be that this was the straw that broke the camel’s back in terms of you questioning him.

The important thing is that, if he decides to reconcile, you should put aside that fear of abandonment (“how do I stop him splitting up from me?”) and figure out whether marrying him is a good idea. I would postpone the wedding and get into individual and/or couples therapy. You two have some really big problems to just gloss over and get married. Divorce is really, really difficult. It is much better to be as sure as you can that you’re in a solid, healthy relationship before tying the knot.