Am I over him?

I have a long history with a certain person; let’s call him Joshua. We met five years ago, and have had an on and off relationship ever since, more off than on the last three years. After the first two years, I was finally forced to confront myself with the fact that we were not good for each other. The way he lived, his lifestyle, ideals, and goals were painfully incompatible with my own. I ended contact, and found it necessary to move to a different state to successfully end the relationship (the connection was inexpressibly strong). However my precautions were in vain, throughout the following years he proceeded to re-emerge in my life numerous times, the second to last of which resulted in an unplanned pregnancy, and the last of which ended us forever upon my informing him of the abortion I’d had, and considered the only option.
In the months following that last episode, I determined that I was over him; I still loved him and couldn’t quite manage hatred or resentment, but I knew that we had the power to hurt each other immeasurably, and all of that pain had sort of made a scar. When I thought of him, I didn’t feel anything; the place in my chest that used to feel the stabbing pain of separation felt as if the pain had never been. I could even look back on the whole thing grateful for what I’d learned through the experience and for the memories I had of him that were still beautiful to me.
And then just recently, I received a phone call from Joshua informing me of his impending role as the father of someone else’s child (I still cannot formulate a reason why he would have told me, what it could have meant to him for me to know?). There are no words to describe the feeling those particular words created in me. When I call his number, a woman who doesn’t sound much more than a child herself says “hello,” and I feel instantly, horribly nauseous, my heart is beating extremely fast, and everything is falling apart. It’s to the extent where I’m physically ill for several days, and for several days after that numb to the point of being completely unaware of what is going on in my life (missing deadlines, unable to process information or have conversations, etc).
I’m back to functioning in a relatively normal way now. It’s only this, that on the rare occasions when I let myself think of him, first there is this gut-wrenching feeling, and then there is the even more terrifying picture that invades my mind-- it’s of Joshua and I, together, along with our daughter (the one I’d pictured before, the one we didn’t have, but younger.), and his child with this person I don’t know, who, in my mind, would be my step-son. What makes this picture most terrifying is its direct resemblance to my sister’s relationship with her husband (most notably their step-son, and their daughter together), and the fact that one of my motivations for ending things with Joshua was the dysfunctional parallel I saw between the two relationships even at that time. Their relationship is something I’d sworn to myself I would never allow myself to fall into. Whatever this is, this feeling I can’t understand, it seems to have unprocessed what I was confident I had processed, and threatens to rip my world-past, present, future – completely apart. I need to know what this is; am I over him? Is this reaction normal, or does it necessitate some kind of future between the two of us? And, if so, is the reaction I have to that picture irrational, or would a future between us be as disastrous as I feel it would?
I had considered sending this to an advice columnist, but then remembered that my problem may not mean anything to anyone there if it isn't newsworthy or the right length. Maybe some of you have experienced something like this and could help? I would really appreciate it.