The problem is that children tend to not believe it when grown-ups say that no, their presence is not why the parents are fighting or divorcing or stuff like that. The Lynns of the world would see this as a sign that the kid thinks too highly of himself and matters more than he matters. Normal people realize that Lawrence believes that if he were a better, more likable kid, his mother would have gotten him a dad by now because kids tend to not notice that while a Ted might want to be a dad, he might not want to be Connie's husband.
The other contributing factor is, I should think, overhearing things that Mother doesn't realize he's listening to about how if she didn't have a kid, it'd be easier to grab onto a man. It took Lawrence until he grew up to realize what that meant is that it wasn't his kid radiation scaring men away that was to blame as such as it was men being too insecure to want to have a reminder that Wifey had a past that didn't have them in it that's the sticking point.