Well, I don't know him but how much can you trust someone who is with two women. A polygamist, at least tells the wives about the other women.
If ever he did want custody, although you have been/will be the primary care taker, I don't know how good it will look that he has provided everything for you- your house, your car and your financial needs, even so you do not work. If it turns ugly enough that he fights for custody, I'm sure you will be out of a house and his money so you better be stable on your own or you won't win.
Also, as far as protection against his wife finding out, what does that mean? You said serves his wife right for having an abortion without telling her husband, well what do you think would serve you right for getting pregnant from a married man?
BTW, how is his wife so horrible for not be honest with him about the abortion, yet he is so wonderful for not being honest about an affair and love child??