In the early days, back when both their marriages were new, they met only by chance. They'd meet up at functions or other boring activities and they'd talk for a moment—after all, they've known each other since primary school. They weren't close back then either but making nice was expected of them so that's what they did.
Carol got pregnant first. Liz was jealous because all she really wanted in life was to be a mother and Carol was besting her at that too. In the month and a half before Liz found out she was pregnant, she refused to even look at her. But when Tyler was born, a very pregnant Liz went to visit the new mother, bringing flowers; and a month and a half later, Carol repaid the favor…and she brought a small teddy bear for Caroline.
When Caroline turned two and John, Caroline's father, was becoming less attentive, Liz called Carol. Carol would bring Tyler over to the house and the two would spend a few hours watching their children play together comparing notes on motherhood. As a rule, they never discussed their respective husbands.
When Tyler was four, Carol and Tyler stayed with Liz and John and Caroline for a week and two days. Carol had come knocking on their door in the middle of the night, mascara running down her face, and Liz prepared the guest room while Carol put little Tyler to bed with Caroline. No one ever brought up the reason for the stay, but Liz stayed up with Carol each night and comforted Carol while she shook uncontrollably as they listened to the phone ring over and over again. On the fourth night of Carol's and Tyler's stay, John left the house and tried to talk some sense into Richard and stayed with him until Carol's departure.
For the first three years after that incident, Liz often brought Caroline over to the Lockwood's and Carol and her would visit and watch their children play. But after Tyler's eighth birthday party when a drunken Richard crashed their play date and accused them of doing 'unnatural' things together, an incident they neither acknowledge nor discuss, they stop with their visits.
Even still, it's Carol who comes around to comfort Liz when the divorce goes through and the moving truck is parked outside the house. And it's Liz who helps Carol thorough her husband's death.
They never talk about all that happened between them in those moments they were alone together, but that doesn't mean it didn't happen and deep down, they both know that.