Suggest departure.

After watching her giant bosoms jiggle in your face for a minute too long, you grind your teeth together and speak up.

"Ah... We should leave soon, Kimi. The water's really cold anyway."

"All right. That sounds fine! Let's just throw some rocks, take in the fresh air, and then we can go~!"

You nod, and the two of you proceed to spend just a bit more time at the river, though luckily with slightly less sexual tension than before. You need to remember that she thinks you're not interested in the female form, but you definitely are. Five more days of surviving this and nobody needs to find out you're a phoney.

Finally she walks up to you and announces, "I know how we can warm up! We have a hot tub outside the back of our house. That'll be a great way to end our second day together."

You smile and nod. Perhaps that'll be better anyway, since you'd both be sitting and relaxing. You both pack up your things and start to walk home again. You watch her from behind, biting your lip as you try to resist thoughts of taking hold of her body and just...

You shake your head. Before you know it, you're almost home.