The past is past. You need to decide if you want her to stop seeing other guys now, or if you just want her to be more discreet about it and stop rubbing your face in it. It's entirely fair for you to ask for either. There are plenty of couples with open marriages where the key to the deal is that they don't flaunt it, don't talk about it.
As for people who ask about your son, you've already given a good answer: "He's not my son but I love him like he's my own." Now turn it into a best answer any real man can give: "He's my son, I love him, and that's all." Say it like you mean business and they'll get the hint and shut up. You'd have the same answer if he were adopted.
Good luck to you. When I read that you were standing by your new son, I knew you were twice the man of the guy who knocked up your wife.
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Old enough to be your daddy
