The angry phase you mention is something I've experienced multiple times, exactly how you describe it. I've made the mistake of sending messages paragraphs long about how I was angry about how they did this and that. I still get that temptation now, and it's very strong. Ultimately, nothing whatsoever good comes of it.
From experience I'm slowly learning to fight the urge to send those sort of messages, and to chase someone who doesn't reciprote your feelings. I find it incredibly difficult, but I think it comes down to personality types. Some can maybe "get over things" more quickly, if they are extroverted types who can be easily distracted. Those of us who have a tenancy for introspection, introversion and close relationships with a select few, it is much more difficult I think.
It's cliché, and seems like empty words, but finding something that genuinely makes you feel good helps. These activities will always be momentary in terms of alleviating sad feelings. You unfortunately cannot hide from the reality that when your head hits the pillow you'll likely think of that person and these feelings of sadness, anger or frustration will inevitably arise. But feeling better about yourself through activities which make you feel good, be it exercise, reading, learning, socializing or whatever, help reduce the time you spend mulling over the past and ultimately help you heal. You'll get there and it won't take as long as it feels right now.