Really the only new things in the game involve stuff at the mall/theater and of course the pool with Crystal. I'm not sure what kinda of walkthrough is necessary here as there are almost no opportunities to build up lust after you go to the pool. Most of the rest are obvious, but if not a couple things:
-Buying swimwear for yourself gives you the most lust, prob what you need the most
-If you play as female opt to look at Maddison while changing, then kiss her then pick the middle option for most lust
-Doesn't much matter what option you pick while swimming, just pick ask lifeguard for lessons after
-During the holding your breath part, pick i'll watch out for you then then wait till her face looks really strained (4th wait?) then pull her up for max points
-The 2 good diving options are cup and squirtgun, I've never got Maddison to pick anything else up
-When chasing after Crystal, try to corner her unless you're a gym instructor in which case say you'll handle it
That should get you to hot tub scene with crystal, afterward check on girls if you are male or kiss Maddison if you are female. From there you will get the scene if your influence/lust points are high enough. If you don't get it, try to get more lust earlier either by hoping you get good coversations at bars or use the exploit where you can bowl over and over again.
Only other new scene is on the train, where you really can't fail but each choice leads to diff option, and at the end if you are male you can choose where to cum on her. Either way if you get to the train you can't screw up from there.
My personal recommendation is to beat the game normally then change the variables or check files to make subsequent playthroughs easier
-