A significant number of women whom I liked ended up marrying the next guy they started dating.

So, you're not alone. All of us remainders are in this together.

And surely you are aware that when a guy takes after another person while he’s already in a relationship that he’s not capable of making good decisions and not worth your energy or consideration because he’s just going to do eventually what he done to you to her so you deserve much far better and should set your own priorities and standards higher than to want a guy that would fall for a tramp outside of the relationship anyway.

This used to happen to my older brother but he got married eventually and was fine

Are we talking about initial meeting? Maybe he saw someone he preferred and maybe someone will prefer you.

You may need to be more assertive.

It’s because they have no self respect nor self esteem to go out there and get their own instead. They are so insecure and have low standards. Not your fault at all to be honest.

maybe you need to be more proactive

for me, I was done with the girl, glad someone snagged her, so I could find a brand new unused one, like trading cars,

Try your hand at other women you may get lucky lol

Nobody can be taken if they don’t want to go. When someone is truly interested in you, they’re not going anywhere.