Why do guys act so erratic after break ups?

Specifically, when THEY initiated the break up? I'd get it if they were broken up with, but to see such confusing, mixed behavior from them when THEY ended it gets a little baffling.

Some friends and I were discussing exes and weird behavior on their parts and had noticed that in a few instances, they were kind of all over the place. Nice, then weird, then kind of rude, then nice... Rinse and repeat.

Why bother to keep in touch if you're just going to be all over the place emotionally and treat her like crap by dragging her through more emotional confusion? I'd think that the person who was broken up with would have more emotional issues like this. I know break ups affect both parties in various ways, but it's like we're witnessing them emotionally struggle with their decision and they're dragging you along for the ride.

So what gives?
Why do guys act so erratic after break ups?
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