It seems that you already know whats the best course of action . . Love works pretty much like physics - the more force you generate in one direction, the more equivalent force is generated in the opposite . .
Remember the basic qualities of love: love is kind, it is unselfish, dot dot dot - Basically love is sacrifice for another - giving up something for another person that the other person may be happy at your expense.
Based on this, the ultimate act of love would be to let go of someone you hold dear, knowing that they will never be with you again. If your guy has lost interest in the relationship, there's not mcuh you can do - trying to force him to like you - feeding your anxiety by stalking him won't really help you. The choice is his, not yours, isn't it?
So why worry about such things? Its beyond our control . . If you truly love this guy - you'd do your best for his hapinnses, even if his happiness does'nt involve you. I felt so much better in this way, knwoing that I sacrificed something, for the better of my ex when I got dumped in the past . .
Maybe what you need is a reality check - get back to earth, and use your logic - At the moment, your emotions are getting ahead of you, and your logic is taking the back seat - it takes a lot of willpower to be able to bridle our emotions, but that is the best way we can go . .
You may want to speak wtih him heart to heart on this, but prepare yourself for the worst, and accept the truth whatever it is . .
And as always, whenever you feel like losing it, take a deep breath, inhale, exhale . . go find a friend or somebody you can rant on, take a nature walk - you'll calm down. Time will heal most of the pain, you just need to do what is best for yourself - Chasing him around isn't really going to change much, and if he finds out, its even worse. . You know all this . . you know what to do . . So pull your guts together and do it! Don't let those thoughts cloud your mind - once they appear - clear them out - do something else - think of what is best for yourself and stop daydreaming . .
Revenge won't change anything - he still won't be with you. So don't waste your precious energy on something that won't do anything . . This new guy at work . . it may help you get over it - but if you jump in again - remember whats most important -
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The key to victory is the element of surprise.
When that doesn't work, I guess I just gotta gun you down.