19 in one go!
First off, Bravo on the game, Pseudo. Very nice. Excellent sprites, scripts, lines, humor, and so on.
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Now, for the quick info.
In order to get all 19 achievements by only starting one profile, simply go through the game without doing much. IE don't get dressed, don't shower, don't do any of your jobs, don't buy any gifts for the date, etc., and be certain to go in at least one pink door per level(the first one is to the left of the attic door, the second right outside of Clarence's house, the third in the park, the fourth below clarence's computer in the second room on the first floor, the fourth at the beginning of the last level, and the last one outside of the restaurant.) When you get to your dating session, just be yourself. Your first priority is to get the worst ending, which you can't do too much for the date. There are four higher endings: Bad, Neutral, Good, and the Best. Just work your way up by going back through the pink doors after each ending, and then strive for 100% when going for the
best ending.
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I hope this helps anyone who just started playing. Good luck on the future flash games, Pseudo, and I wish you a nice day as well.