Why wouldn't he, he was divorcing his wife.
1. He was trying to hide his existence from Steven. Dating one of his co-workers would be at odds with that aim.
2. Steven was the dominant personality at the time, with Marc only managing to borrow the body for finite periods. Given how serious Marc is, particularly about his mission, how likely is it that he would take an evening off to have a date?
3. Does he actually want to divorce Layla? Or does he just want her as far away from him (and therefore danger) as he can manage? I don't get the impression he is really "over" their relationship at all.
Maybe it was Marc. But there seems to be enough there to suggest a third personality may exist.