Why do women seem to get more serious with a man if he turns down physical advances?

Has happened to me twice.

both girls would tease me in a lighthearted manner. Then later they started to touch me, which i think is a sign that they were interested. In both scenarios i backed away because i felt awkward.

after that happened, both of those women stopped being immature and got more serious. No more joking or teasing. They shifted to being more serious, but they would still talk to me like they did before, just without the joking.

Why do women seem to get more serious with a man if he turns down physical advances?
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