My interpretation is that after she sucked on his fingers, he jerked off until his hands felt like they were going to fall off. Like any sane human would.
@Shigeruguy I thought that her sucking on his fingers caused the swelling. also if he was so afraid of being exposed for sleeping in the same bed as her, imagine being exposed for jerkin it in the same bed.
I can't help but think of this situation realistically, i. e. given that his fingers are swollen, she kept his fingers in her mouth for a really long time, and I just think that while the finger sucking would be really arousing to start with, after like 30 minutes it would just get annoying and gross.