You can meet a guy who has child/ children too.

You acted after responsibility not after selfishness.
You actually don't know how a second child would be.
They don't come with warranties.

Dream for a while a life of single mom with 2 difficult children from different parents.
Can still see the reasons of your choice?
I can.
What if the eldest wouldn't accept him / her and become even more difficult, just because of this?

Now you are telling yourself that maybe this second baby could be perfect and would have added joy to your life. We don't know that. It is possible, but there's no certitude.

Compared to the lots of men and women who just 'have children' because everyone do so, I lift my cup to a responsible mom who could think before and choosing what she thought best.

Have i seen tons of damages made to kids by irresponsible parents!!!

Cheer up!