It's always okay to block someone but you can always just say "thank you but i'm not looking for anything right now" if you fear of retaliation from the blocking, it lessens the blow and even it is him it doesn't make him at fault (it sucks to have to do but sometimes if you worry about safety precautions should be taken)

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if you fear for your safety you can do like whatever you want girl. block him, ghost him, whatever makes you feel secure.

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