Cynicism stems from not wanting to give one's life meaning or refusing to see any meaning in one's actions. It has not much to do with personality traits.
Introversion is one of the big five personality traits, it can be measured and it is mostly heritable.
Depression, pessimism and cynicism do not cause introversion.
Just like being pessimistic or cynical will not cause depression.
Depression runs deeper than that and is either caused by real events which happen outside of you (not having a job, friends, a girlfriend, a purpose, a healthy lifestyle, etc.) or by a genetic disorder.
I believe you're conflating a lot of notions.
I also believe sleeping around is also harmful for guys, but much less than it is for women.
In any relationship, you never want to be even the "second best guy" your girlfriend has ever dated. This is the main reason all religious texts strongly advocates virginity for women. They also ask men to remain pure by the way, but it is not stressed as much.
And I believe there are reasons for that, men did not pull these religious stories out of their asses, mythology was never random too, the archetypes found in mythological or religious stories are still valid.
Can you follow

? I guess my main point to your counterargument "but why does it matter how many guys a woman has slept with" is:
I believe that
everything matters to an extent. The simple fact that we're discussing it should indicate that it matters. Now there are no easy answers, but arguments can be given to support each side.
I've been with several virgins in my life and I agree with you that some experience on the part of the girl is preferable,
unless she has been with a guy who's better than you, that she perceives to be better than you.
Then that relationship is doomed, and this is why I believe a woman partners' count and quality matter.
Allah o akbar!