You can share things with him only if you fee comfortable doing so. After all, you were separated and each one led their own life including him. What is most important now is that you are together and are working on your relationship. It is doubtful that he would have expected you or anyone else to remain single once he was out of the picture.
Just think that there may be things that he has not shared with you in regard to the time spent apart. Instead of feeling guilt, try to focus on being honest in the present time and building a solid relationship this time. Afterall, you are both young and you had done nothing out of the ordinary or shameful dating other people. Those experiences had helped you realize that this time you want to give this man another chance. That is what matters in the end.
If you decide to share your past with him, that is still a decision you will have to make and his reaction to the information will help you know what kind of individual he is. If you decide not to share, that is also your right and anyone should respect it.