Yes, no, maybe so

This one has a bit of a story to it, but I think it helps to know the whole situation. So two years ago, when I was still in high school, I met a boy. He was cute and sweet and alarmingly introverted. In those first two months of knowing him, he only spoke in one word sentences around me he was so shy. Still, he caught my attention. So we started texting and became friends. Then we started dating. We dated for nine months, though admittedly we never kissed (both of us too awkward at that point in time to make the first move). At the time I was personally in a really bad place, and ultimately I took it out on him. I neglected the relationship and felt smothered when he expressed the want to spend more time with me and dismissed his feelings. The only time I've ever seen him angry came around that time, as he was resentful, and rightly so, that I was not giving him any attention. And I mean any. I didn't treat him like a priority at all. So he was upset, and I felt smothered. So despite the fact that we both cared about each other very much, I broke up with him. I did not regret doing so and I have not since. Yet he and I still remained close. In fact, just as he was then, he is still my best friend, and I honestly could not imagine my life without him. Fast forward over a year since the breakup. Best friends still, albeit from a state away as I left for college, but we still text every day and on the weeks when I am home he practically lives at my house. Yet as good as things are now I never did apologize for how I treated him back then. I would do so now, but I am worried that that will stir up old feelings that we really haven't talked about for so long. And it is not as if there are not feelings still there. It is plain to see that he still has serious feelings for me. And if we're being honest, I still have feelings for him(that's putting it lightly). This is sure to make things difficult come this summer, which we will be in the same town for the entirety of until heading our separate ways(me back to school in WA, and him starting in MN). I know that any dating between us as the people we are now would not be casual, but I also know that I am not really ready for that kind of intensity quite yet. I also know that long distance relationships are plain awful, and that is what would happen after summer ends. And there is a reason we broke up in the first place, and the last thing I want to do is be the cause of any more pain for him. Now is not the right time for us, but I do not want to lead him on or hold him back. Do I wait to apologize for how I treated him back then? Do I tell him what I am feeling and thinking at the moment (pretty much everything I've said here)? Do I wait for a better time for us, or should I encourage him to get back out there? Could I even casually date during the summer without hurting him? Or is it best that I keep my mouth shut and keep the mingling to a strict zero this summer? Any advice would be appreciated.