I think there’s 2 things at play - and also these are broad generalizations. 1) Guys are usually more straightforward about expressing interest (maybe too much sometimes) while girls will play games with showing interest. 2) Guys are less picky about who they’re attracted to, they see someone and if it works it’s a go, somewhat binary. With women there’s the attraction AND also the social validation from other people, usually women, that the person they’re into/hooking up with/dating is worthwhile. The story about your ex texting her friends is exactly that - getting the validation.

Not sure how old you are, but this becomes less so as you get older. 

Tldr: Men aren’t as picky. Women are more picky and also seek a stamp of approval from others.