I'm angry that my girlfriend shared a bed with other people before me
Why are you mad about something that happened before you were around?
I can't believe that there were so many guys that she's been with.
Still though, this happened before you were around. You should not be that upset about things that happened before she knew you.
I'm not over it, she's been with too many men.
Unless she has a sexually transmissible disease that she caught from those other men, I do not think that you have the right to be angry as she will surely not judge you for who you have been in the past. If you think you can't be okay with what she has done in the past then I think it is more okay to just break up with her, as you may hurt her feelings later down the line in your relationship.