My understanding of is he was happy up here and his wife was all set to move the family up. However, he was shagging that bimbo off the radio that half the team had gone through. He had told Tony Adams, his mate who told his wife. The two couples were very close, often going out together so Mersons wife found out through Tony Adam's wife.
She wasn't coming anywhere near the north, and he had to leave in a hurry and go home to Birmingham (the family home was in St Albans).
Anyone who remembers at the time, Merson had been in the wilderness and had resurrected his career at the Boro, to the point that he had been called up for England. He was in fact away with England when it all blew up, with him being interviewed on tv and making the first claims about the drink and gambling. But, it was Tony Adams, who was also asked about this while with England, who let a couple of things slip which let the cat out of the bag.
Sex, not drink and gambling, because the drink and gambling never really stopped, did it?