Why the sudden change?

Me and this guy has been talking for a month as of today. He was doing everything that a person would do if they were dating. Literally doing all the things you would do to your girlfriend/boyfriend. We weren’t intimate at all. The only thing we did was kiss. But today while at school, I seen him talking to his ex whom he stopped talking to months ago. So I asked him what we were because I just needed clarity. He told me that we were just chilling, just feeling each other out. He also said that he didn’t want anything serious. So I just told him this wouldn’t work out. He then asked me if we could at least still be friends and I just told him no flat out and never spoke to him again. I’m just confused why the sudden change? And why would he want me to be his friend after wasting all of his time, energy and money on me?
Why the sudden change?
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