you probably did the right thing breh. I understand we all have emotions and aren't robots but there's a difference between acknowledging (and managing your emotions) and being a slave to your emotions. IMO the key to happiness is to find ways to manage your emotions logically. Chick had a kid. Father is still in his life. You could probably see all the potential drama and issues. and although she could have been a cool chick, you probably felt like you had better options in life.
you got the other girl. you prefer the first girl BUT you prefer the second situation or "package". You did good breh cause the second chick is still a great girl as you said.
remember one thing in life breh. There is no such thing as "unconditional love". The sooner you realize this, the happier you will be. Don't let people try to guilt trip you into "if you would have loved her you would have accepted her kid as your own"
You loved her while you were with her but you felt like it wasn't right for you. now the left over emotion is attachement. advice i'd give you is to try and focus on the good things your wife does for you (without comparing) and whatever you would like from her to be happier. Maybe you'll realize that your wife has an even bigger potential to support your happiness than Kay ever could.
Personally, the only way i could be with a single mom is if the father is dead (even then i probably wouldn't unless i have no other option but that's the only way i would consider it.)