It's like a inverse harem game. You start out fucking a lot of girls, but eventually you are going to have a choice to make.
That choice might or might not lead to an ending with multiple girls (Katie, Lily, Debby), but there is no way the game ends with you being able to continue to fuck everyone.
As far as Jenna goes, anyone who really studied the images on her computer can tell that Jenna knows a lot more than she has let on.
For instance, the image she has from your laptop is from the morning Katie dry humped you on your bed. So she already knows you're involved with Katie as well. She has also been watching her mom's Laptop cam, so who knows what else she might have seen of you and Monica in bed. Finally there was an image that appeared to be Bella in Jolina's kitchen. Which means that there is definitely something to not trust about those two.