"Don't worry, he won't be able to find Betty, me and Stanley, we won't let him find her. What's more, I talked to Betty about this matter, and she said that she won't be curious about Calvin, and she won't think about seeing him. As long as she isn't curious about him, then she won't fall in love with him once again."
They say that falling in love with someone basically starts with curiosity.
The current Betty forgot about Calvin, but Betty knew that she had loved him in the past and was still deeply in love, so such her was the most curious about George.
But at the same time, Betty knows that she loved Calvin in the past and loved him very painfully, so she also restrains herself from being curious about him.
All in all, half safe, half dangerous, she guessed.
It was up to Betty herself to restrain her curiosity about Calvin, if she could restrain it, then she would not fall in love with him, if she could not, then everything would be in vain and it would be back to square one.