You are the one that knows him and can judge the situation.
Does he spend lots of loving family time with his woman?
Even if they seem from the outside looking in like a blissful family behind closed doors that may not be the case!
Not all men are bad, wankers, scum etc, etc as said here before and lets remember there are plenty of women who cheat on their partners.
If they are doing it them something is lacking in their relationship other wise they wouldn't do it!
Most people in that situation only stay together for financial reasons - SAD!! Using the kids as an excuse, do you not think it hurts kids more to see unhappy, unloving parents?
Why anyone would live a life of misery for the sake of money is beyond me!
I think it's utterly unfair for people to say you have no self esteem and self respect, it sounds like they've made him in to a monster and you out to be a nieve little girl - which from your posts I don't believe you are and I'm sure you have lots of self esteem and respect for yourself.
You are a good mum but you have needs too!!
It's not always about your kids!!
Ok you've been hurt, join the club, but you know what it's done you can't change it so put it behind you and move on looking forward.
And yes being a young single mum with a small child can be lonely but you know what - it doesn't last for ever it's just a small part of your life and it does get much better and easier.
Go for it girl, enjoy it, it might not last for ever but if it makes you happy for as long as it lasts then it's been worth it!
Best of luck remember it's not all doom and gloom, you are not a bad person and neither is he you just want love and to be happy x