3 serious ones, my first bf I was with for nearly 7 years (he was such a horrible person but I was young and didn't know any better), and I was with my 2nd bf for 3.5 years - I was engaged to both of them, bought a house with the second one, and also got as far as actually booking a wedding with him too, but then split about a year before it was supposed to happen. 3rd time lucky for me!! I've been with MrDD for nearly 9 years now.
He's only had one serious gf before me as far as I know.