What is "the thing" that makes a man or a woman feel the attraction of one man/woman over the other one?

I present you an example

A woman is introduced two guys. Both are not super attractive, they are in their mid 40´s and both single never married or kids either. They are just average looking. For some ladies maybe in their perception they are hot physically but they are just average common guys. The lady knows the two of them and she is not dating either one or or a in a relationship or anything like that, but the lady know both. One of them treats the woman super nice, joke with her, he is her friend, sometimes he is a bit flirteous and tease with innuendos about woman, sex, sensuality, etc. After all he is a guy. The klady do get along well with this friend and whe they both have to go to the gym together since they both go to the same gym and are member of a sports team they both go together to train. In any moment the guy had made passes at the woman, like suggesting to get laid or any of that, never of that the guy had done to her, he jokes with her about men sure but they get along after all. Here is the difference: The lady does not feel remotely attracted to the guy as a guy. They do get along have some kind of chemistry but only as friends but she does not see her like if he will be a potential or future boyfriend, The text each other often but only as friends. Some could sy they could make a nice pair knowing they both get along, they are in the same age group, they know for years, they have friends chemistry but for hte lady she does not feel "this attraction" for the guy as to treat him as he could be a a boyfriend. SHe does not feel that. Also the guy never had hinted her he wants them to date. she doe snot feel "that thing" that could make her feel attracted to the guy for something more.

Then it comes the other guy the "bad one". This other guy the lady know him for 5 years as this guy awaken "things" she did not ahve she had until she met this particular guy with
8 mo
first guy sh neer had awaken anything. Around this second guy the lady feels nervous, she wishes she never leaves when they are together ( like family social events as the guy knows some of the ladys relatives and he is invited). She feels for the guy this attraction that with the other guy she never had felt. With this other dude they both had made out and she had loved it. Sh feels very drawn to the guy even if they do not even see each other often unlike the other guy that she do see him
8 mo
more often for sports reasons but this second dude had made her feel things other guy has not, he also had joked with her, senusally also like the other dude. She feel things she dont understand but the guy is unavavalabe not that he has a girlfriend cause he idoes not have one but the guy sees h er just a friend to get laid with.
What is "the thing" that makes a man or a woman feel the attraction of one man/woman over the other one?
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