Guys, What kind of behavior does he take when he likes me?

I'm female. He and I are online friends and we've known each other for a couple months. At first we were texting about casual stuff. But recently I've noticed that he often asks me for my pictures at night. I know it's natural to send a pretty picture of me because we are good friends, but he asked me to send him my thighs' photo tonight for the exchange of his thighs' photos. He's making it lewd. Do you think he is just using me for his own purpose? Or is it normal to do that with male friends?

Guys, What kind of behavior does he take when he likes me?
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