Guy disrespected me and doesn't understand why I rejected him?

I was dating a guy I knew for years and he bragged about sleeping around ( I don't know why he did it , I immediately cut it off with him because he doesn't understand how much that hurt and disrespected me ) he keeps reaching out to try to date me or contact me not apologizing for that.. I told him I don't need a std and he says he's been tested with a clean board of health.. the issue is I no longer trust him since cutting him off.. a 15 year relationship is gone and he says he wanted to marry me.. I don't know he said this to upset me or playing childish
Guy disrespected me and doesn't understand why I rejected him?
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