Chloe’s dalliance with Philip is really none of Carly’s business. However, Stephanie trapping Nathan by getting pregnant could ruin the rest of his life. He definitely needs to know where it wouldn’t affect Daniel one way or the other if he never finds out.
I just finished reading The Sunday Philosophy Club which presents a multitude of ethical questions and the one Carly is facing is certainly a good one for discussion. There are excellent reasons on both sides for whether she should or should not tell Daniel. I can see where the case could be logically and ethically argued either way.