Obviously because nothing is your fault, you have no control over your own body, your own decisions, your own life. Everybody else is Fn you over and everything is happening to you right?
Seriously, I'm not actually trying to make you feel like crap and I'm not trying to even beat you up. I don't know you or anything about you. I just see/hear the same thing over and over these days, no one takes responsibility for their own lives and actions. Everyone thinks life just happens to them.
I don't think you are a bad guy at all, you kind of come off like you have an attitude but you probably have reason to. You claim you work hard and you love your boys and try to provide for them, I'm certainly not going to get down on you about that.
However, going back to before any of this happened, you had choices in your life. You chose to date this woman, you chose to continue doing so, you had to have gotten to know her and know what she is/was like. You chose to sleep with her before either knowing her very well or marrying her or getting engaged. You chose to not have one but two children out of wedlock with her, you chose to support her and let her get state aid and not marry you. You see what I'm saying?
You could have dated a girl who was more like yourself with the same ideals and goals, you could ask her to marry you with or without a ring and "wedding" and if she said "no" you could choose to walk away from her. You could have not had sex until marriage or used very good protection until you were ready for kids, married, and/or could at least afford them. I know there is nothing you can do about any of this now. But just whining and complaining about how bad your life is and how you are getting screwed isn't going to change anything either.
So really, I wish you luck and I hope you and your family can work everything out and get on the right foot.