Its a tough one. I'm a bit progressive in my relationship views, so you can take my advice or leave it, I won't be offended.
I'm certainly not going to imply that this is your fault, but you did say it yourself... you're jaded. Its perfectly normal; you've been unbalanced by a guy who left you when you were pregnant. So, you are confronted with the seemingly unfathomable task of finding love. Its not that bad

First of all, don't think for a second that you are any less desirable because you have a child. Trust me, if there are guys out there who won't date you because of a child, they aren't worth your time anyway. With all due respect, it is a person's choice... if they don't like kids they are free to think that way, but they aren't the kind of guys that you want anyway. Its no different than if you are a certain body type or ethnicity. Guys gravitate toward what they want and having a child is an attribute no different than being Asian or short. I personally really don't dig children, but I've dated many women with children, because my relationship is with HER, not necessarily the kid. If a woman wants to introduce me to her kid, that's great. Its no different than any other woman introducing me to her best friend. But as soon as the talk surfaces about providing for, caring for, or "can you support..." I'm gone. At that point, I realize that she is not looking for a loving relationship with me, she is interviewing for a new Daddy. Sometimes you get guys who WANT the job of Daddy and that's great, but you can't ask for it. If he freely gives it, fine, but you and your child are your own humans. He is not required to love your child any more than he is required to like your best friend.
You've probably heard this a million times, but you first of all have to own it. Love your situation. Love yourself. If you are looking for someone to complete you like Jerry McGuire, you'll fail EVERY time. There is a fine line between loving someone and needing them to be yourself. You don't need a partner. Your child (despite what everyone from the 50's says) does not need another parent figure. Even moreso, your child would be worse off with a poor parent figure than none at all. If you need a man to help pay the bills, help raise the child, or complete your heart, its just not going to work. Your sponsoring thought is very important. If you want love (who doesn't) then go about it as a search for love, never as an expectation for a supplemental parent.
Lastly, (and this is true for ANY relationship, but particularly important for you) don't expect ANYTHING. Too many people enter a relationship like getting on a highway. The on ramp is dating, the highway is a committed relationship, and the destination is marriage. Some relationships move fast in the passing lane, others move slowly in the right lane. I've had so many relationships fail because one of us (not me

) kept expecting to move to the next level. If you meet a new friend, you don't expect them to end up as your best friend in a certain amount of time, you're just friends. You have close friends that you met last week, and occasional friends that you've known since childhood. As soon as we mix sex into it, suddenly its a freeway with a destination and that is a killer. Don't try to make it into anything. Its OK if you drive slowly, or stop for 3 months at the rest area because you like the surroundings where you are. Heck, its fine to get out of the car and leave the guy if you and he don't agree on how fast to go. Just be pragmatic about it by being honest with each other and yourselves. If you want to get married two days later, go for it. If you'd rather be best friends with benefits for the next 35 years, that's just fine. I've had relationships where I was naked with a girl 2 hours after I met her, and I've also been in relationships for 6 months where we never had sex. We both really enjoyed the depth of our relationship where it was and never got to the point of actual intercourse.
At any rate, this old friend of yours may be a wonderful viable friend, maybe even more, but you're talking trouble. There is every possibility that you could have a very valid and wonderful relationship with him, but the odds are stacked against you. He's married and looking to supplement his intimacy. You are a jaded romantic. That has the potential to ruin a lot of stuff. Do it right, be honest, and don't be the enabler of his violating his contract with his wife.