Once you reach the points threshold there will be an event you have to pop in your bedroom to open up the next level of points. It will tell you exactly what you need to do if you open the computer in your bedroom, click on the "Check your progress" tab and then the character portrait, which will open up the screen below:
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So to open up the possibility of the event being accessable in your bedroom you will need:
Raise her love points: 600/600 (which you have).
Raised the clothing level to 2: this is completed by going shopping with her at 8:50am on a weekend by speaking with Jen in the hallway, then completing 3/3 events at home which will raise you to the next clothing level. This can be done at meal times or during yoga.
Buy her some new clothing: Same as raising her clothing level.
Once these things have been accomplished make sure to sleep. Then the next day at the appropriate time and place (this time 19:00pm-21-00pm) you will get the event to level her up to the next threshold (which is 1000).
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Just to be super helpful I'll also go over the 1000 point threshold as I've got the game open and 15 minutes until my food is cooked:
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So this is the big milestone, after this the daily events at home and work will change (if Jen is your assistant) and more fun can be had. So you need:
Max her love points: 1000/1000 (self explanatory).
Money: $200/$200 (same).
Buy some smart clothes: These can be bought from the Clothing Store in town for $50 during opening hours.
Buy her a new dress: This is done at the same time (8:50am) as raising her clothing level but it's under the "Formal" tab rather than the "Everyday" tab.
Once you have all these things and have had a sleep another tab will appear in your bedroom at the right time and place, so 17:00pm-18:00pm in your bedroom as below:
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The game functions like this from then on. All the big events are accessed in your bedroom. Use the computer if you get stuck on what to do, or just post here. Always happy to help.