Guys, Why would a man in his thirties act this way?

Show obvious signs of interest, then start avoiding you. Refusing to kiss or sleep with you, badmouthing you to mutual friends, then start following you around everywhere and trying to talk to you the following year?

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Also, what are some red flags to look for early on, before you start dating a man? To stay safe?
Guys, Why would a man in his thirties act this way?
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