Maybe I should rewatch the beginning of the show, as my memories are getting dim, but I seem to recall Ai didn't understand love, despite her name, and wanted to experience it by having kids. So, the man would have been nothing but a stud for her. A walking sperm bank. So, nothing to forgive, really. Too bad she chose a psycho. Although there's always the possibility the man actually convinced Ai of the need to learn what love is and to do it by having kids. And then he had her killed. She wasn't unhappy to give birth to Aqua and Ruby, though, so regardless of how it began, it wasn't a bad decision.