Confusion

This is a follow-up on:
http://www.able2know.com/forums/about31777.html

My ex contacted me two days ago, she'd dumped her new guy and wanted me back. I realized how much I love her, she's the center of my world, in many ways. We decided to get back together and our relationship now is even better than it was before the trouble began and I'm very happy. I also feel that I could spend the rest of my life with this woman. I've wanted her back, just like this, for so long so the other emotions I am experiencing are conflicting.
But, since I've been on my own, and since I rediscovered an old flame, as I mentioned in the previous topic, I ended up sending her a card, warm but platonic, later that same day my ex contacted me and now I find myself confused. I love my girlfriend, but I think I have feelings for this other woman as well. Which is strange, as I don't know her well, but as I said previously, we connected. And I'm scared now that I made the wrong decision two days ago, that we should have let things remain as they were. Still, my gf is such a wonderful person and things are so different now. But I find myself thinking of this other woman, from time to time, and it makes me feel guilty, in a way. It's naive, as me and her have never been anything but friends and never been intimate or anything, but my gf needs serious commitment and I'm scared I'm just putting up a facade. What should I do? Should I be alone? Am I just ruining something real for something that's merely a dream?
Fact is, situation was such that my ex would never have remained just my friend, she'd been gone for good, gone from my life for all time. Maybe I was pressed for a decision I shouldn't have made but it felt right, yet I am confused.
Anyone with similar experiences, please share.