Why would a guy who once would not leave you alone suddenly go radio silent?

We are coworkers, he was showing interest and by the time I felt the same way he had entered into a fully committed relationship with someone that he had recently met rather quickly (they met online and moved in together after only knowing each other for one month). The fun bit is he never told me about the new girlfriend and continued along with me as if she didn't exist, when I eventually found out and how serious their relationship was I was obviously horrified and cut off all contact to the best of my ability.

He proceeded create/force meaningless interactions and conversations with me for the next 5 months until the new year where this behavior increased in frequency until March. As of to date he has not breathed a single word to me for 1.5 months, no visits to my desk, no pretending to 'need' things or people near or around my space, nothing.

There were no outbursts or confrontations in this time it appears that his actions were on a incline and then took a heavy nose dive. Don't get me wrong I am thrilled he's finally leaving me alone but what happened? I feel the need to ask the male perspective as this had gone on for 7 months straight, whenever I feel like a can finally move on with my life a part of me wonders am I really free of him can I finally relax or is this calm before the storm? Is he finally focusing on the relationship is actually in or don't hold your breath?

Why would a guy who once would not leave you alone suddenly go radio silent?
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