I am in my late twenties. I'm a "hardcore monogamist" as you described, for the most part & I've had a couple serious relationships (one lasting 6 years!). Though, in between long term relationships, I tend to always be casually dating someone. However, I will not call it a relationship & ultimately give them my commitment & innermost self unless I am serious about them. As for break ups I'm describing, I mean only the real relationships - with a small exception of a close friendship that crossed the line & got way too complicated. That one felt like a break up. I will say that I've been described as the "girl who always has a boyfriend", though.
I agree with --> "Also, aren't people responses in 'breakups' really dependent on what the relationship and the person meant to them and if they are the kind fo person who 'sees the writing on the wall' for a while or is the person doing the dumping?"
I tend to cut off communication regardless of who did the dumping. I need to do it in order to get over the relationship and move on. However, if I am doing the dirty deed, then I don't always go into analytical/self help mode afterwards. I'm usually on the receiving end of the dumping, though, because I tend to stick around in relationships long after they should be over.