Is it normal that i suddenly can't let go?

I was with my ex-boyfriend for nearly 8 years. He's a few years younger than I am, and we work together. We were engaged for about 2 years, but he balked every time I tried to make wedding plans, saying I was "impulsive" and unrealistic.

He broke up with me via text in September, saying he didn't think he ever loved me and basically spouting off about what a terrible person I was. I just stopped texting him and was lucky that we never ran into each other at work. He texted me in November, all emotional, saying he loved me and missed me and was sorry for how he went about things, and wanted to meet me. We met, talked, and made out. From that point on, things were hot and cold. Every so often, he'd have a freak out that he felt we were "back together" and he wasn't ready for that, and I'd cry and distance myself, but he kept coming back to me, I guess for comfort.

Last week, we went out, and he said basically the same thing again. SO I gave him his space and only texted him after he texted me, and kept it short and to the point, nothing personal. I felt like I'd be ok to move on, but now, all of a sudden, I'm crying and missing him like a limb. I saw him today with the person I long suspected of being the reason why we broke up, and was so angry I was shaking. I just feel so hopeless and can't stop thinking about how great it was when I had him, even though it wasn't.

So am I crazy for this to suddenly really hit me now? I don't want to date anyone, and feel like I could never move on, even though I'm old enough to know better and to have had my heart broken in the past. I really feel like I can't go on. Normal?