they both got issues. he has no self-control, lets his baser instincts overrule his rational thought, and she's wishy washy and just goes along with him.
pretty sure its his self-loathing and guilt for tying her down with marriage that keeps him from doing that further by having kids, and officially announcing their marriage to their colleagues. the divorce paper is because he's contemplated setting her free. He knows her as a free-spirit (though she lacks follow though on that).