Bobby did some irresponsible things, but there's one thing that stands out - something he did where he was basically gambling with Pam's life. The gamble paid off but was a crazy risk to take. Bobby brought Christopher to Southfork, believing that JR was Christopher's father. He fully intended to hand Christopher over to JR, but then Pam walked down the stairs and saw Bobby holding Christopher. She looked incredibly happy and asked "You got us a baby"? At that moment Bobby had a choice to make. He could have told the truth, knowing that Pam would be disappointed for a while but that she would understand that the baby belonged to JR (based on what was believed at the time). Instead Bobby chose to tell a huge lie, one that could have ended with Pam confined to a sanitarium indefinitely or worse. He told Pam that yes, he had gotten them a baby. Since he had every reason to believe Christopher belonged to JR, how could he possibly have thought this would work out well for Pam? Supposing what Bobby believed about Christopher to be true (that he was JR's baby), he had no reason to realistically believe he and Pam would be allowed to keep the baby. The most reasonable outcome to expect would be that after Pam had become used to the idea of being Christopher's mother, she and Bobby would have to hand him over to JR. How would Bobby possibly expect that to turn out well? However disappointing it would have been to Pam if he had simply replied, "No, this is JR's baby from Kristen", it would have been exponentially more disappointing to Pam to have to give up Christopher and the idea that she was going to become his legal adoptive mother after several weeks or months of becoming closer to Christopher by the day and becoming increasingly used to the idea of being Christopher's mother. Pam was suicidal before, which is why she was supposed to still in be the sanitarium that day. So considering she was already suicidal, imagine how devastated she'd be if maybe after a couple of months of taking care of Christopher and feeling that she was his mother, she were to find out that she couldn't keep Christopher because Bobby had lied to her and the baby belonged to JR? Pam might never have mentally recovered from that. She may have taken her own life. As if all that isn't bad enough, Bobby would have been found guilty of trying to steal his brother's child. That's a felony and that means prison. It would have been absolutely disastrous for Bobby and Pam as a couple. They were only saved by the incredibly unlikely twist of fate that it turned out that Christopher was Kristen's son from another man who had the same blood type as JR and she had the baby very prematurely which made the time frame work out convincingly. The odds of Kristen miscarrying JR's baby, then becoming impregnated by a man with the same blood type as JR, and then have that man's baby prematurely enough to make it realistic that it was the child she was pregnant with when she left Dallas for California were astronomical!