Can you really stop loving someone in one day?

If you've read my other questions, you know I've been with this guy for a while. We were really close and had a deep connection emotionally. You also know he broke up with me because of a drug addiction. This is an example of what I'm trying to ask about:
The days before our sudden breakup, he was as kind as ever, taking me out to dance on the porch, holding me when we slept, smiling and laughing and talking about living together in another state--then it changed. He was busy with work, I knew, and struggling with his addiction, but then all of a sudden he called and said he "knew" he loved me but wasn't sure if he was "in love" with me. it was as if his feelings disappeared in a day.
He said that he was upset about it for a while, and he talked to me about wanting to get back together one day in the future, then suddenly seemed to hate me just because I found out he hooked up with someone. His friends told me, without me even asking, and they were really upset about it. But he says I'm at fault and it's almost as if his love for me never existed with how he's acting now.

A lot of guys I've dated were really close to me and all said I was their perfect match. Even after the fact they say that. Yet, they all broke up with me out of the blue because they said "I just stopped loving you yesterday" or "you're more like a friend". Seriously.

Why do guys do that? is it even possible to wake up one day and think: I don't love this person anymore. And if they thought like this before, why not say it immediately and work it out instead of letting the girl think everything is ok?
Can you really stop loving someone in one day?
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