Level 5 Love can only be unlocked in Act Three (not currently in the game) and will only be available if you hit level 4 with the girl before Act Three begins :)
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No timetable, I'm afraid. I never give dates for things because I don't want to disappoint people if/when I miss them :P
There's still quite a bit to do (last of the Main Girls getting to love 4, the main storylines converging, pregnancies for a lot of the side girls, college content, etc.) but it should start moving quickly once the Main Girl stuff is done.