Though Peter was aware that Bethel understood the science behind what he was doing--she'd read enough of his papers in college and listened to him ramble on about it over the years--it never occurred to him that she might have already figured out what was happening and why she kept miscarrying. He just didn't want her to take on a burden that wasn't hers to bear: the reasons for her miscarriages. He also wanted her to know so she'd be fully informed and if she wanted to stop trying to get pregnant because of it, he would understand.

He didn't want to make her cry anymore, no did he want to piss her off and he hadn't thought about his guilty edging hers out and giving her a chance to surface from it. That was an unexpected, good benefit.

At first, Peter didn't respond to the kiss because it was unexpected and he was a bit surprised as well as overwhelmed by her ability to love him in spite of everything else. When he did respond, it was a reflection of her kiss, overflowing with love and gratitude for who she was and what they had.