Honestly, how would you feel if he did the same thing to you? I know it sounds cliche as hell, but it is true. If you are talking to him on any deeper connection level (ie, why didn't we work out? do you miss us?), then yes, it classifies as something that needs to be nipped in the bud. Since he is the father of your child ( I am assuming that your husband knows this?) he does have somewhat of a right to at least know how his child is. This is a somewhat sticky situation. Use your intuition. If it feels wrong, then it most likely is. Sorry to say, but if your husband is raising your first born as his own, and your ex contributes in no way (financially, emotional, etc), then it may be best to cut him lose, especially if the temptation to even talk inappropriately is present. I wish you the best of luck and hope you decide wisely.