Their love potion induced affair lasted 10 years before Merope was with child. She thought considering the child was on the way Tom would not abandon her. Over the last 6 years, she had deluded herself that maybe he had truly fallen in love with her. So slowly she weaned him off the love potion and hid away the signs that she was a witch. As the haze cleared Tom Riddle realised what had happened. He didn’t know he’d been drugged but he did realise he was not in his right mind. He apologised profusely to his wife and children and then threw a heavily pregnant Merope out.