Author here. Yes, I've used introversion and extroversion mostly to mean the amount of socializing one does, and that's probably not the best definition of those terms because they also relate to energy. And people are not a perfect binary. I've heard terms like ambivert and "low energy extrovert" which I think describe me well.
One thing you said well is how you put in the effort even though it was an energy drain. Because you felt the reward - finding a partner - was worth it. And I have mostly not felt that way.
That makes sense. And I'll add that feeling the reward was energizing. For whatever reason, I experienced interest from a few girls in high school even before I made much of an effort, and I had just enough success in my first two years of college to keep me going even when it wasn't going well.
I'd compare it to the sport of golf, in which it's well known that hitting just one good shot (straight and pure) in a hundred will keep someone for the next thousand shots because they feel sure that they can do it again.
I'm one of these guys, and yes, I met my wife and we started dating because I temporarily made a very conscious effort meet girls in college. As a CS major and ROTC cadet, I went out of my way and my comfort zone to take classes and participate in activities that had a more favorable male-female ratio. I met my wife in a foreign language conversation group that was at least 2/3 girls after asking a few of them to meet one-on-one for more practice. And yes, I'm sure that my sex drive at age 19-20 was a big part of that.
But I wouldn't call that "[becoming] more extroverted." I think an extrovert is someone who draws their energy from socializing. I didn't. It was an effort, a drain on my energy. I still drew my energy from reading, thinking, writing, listening to a podcast (radio programs back then), going solo to the gym or for a run, etc. Similarly, I can talk to people or do public speaking for my job, but it's still not where I get my energy; I retreat afterwards to the quiet of my office, car, and lunch by myself.