Wait until day 3 you will get the ok. Also if you have the will power you can wait on Liz as well, but that won't be until day 7. You can save her cheerleading path by not having sex with her too. If you want a faithful route just turn everyone one down until Jamie has a certain talk with you on day 3 after school. Trust me it is possible to stay faithful until day 3, but you will have more fun going a cheat route in the long run. Also don't look at the guide unless there is someone you want to see if they have a lewd scene yet until you make it to the end of the current update. The experience is way better the first time with out the guide, then your second run you want that guide to see how to get everyone you may have missed. The game is pretty straight forward with saying basically yes or no to each girl. There are some that are triggered by saying yes to someone on day one, but that is basically for the cheat path route (I highly recommend it for the day 1 scene with Alexis alone).