I managed to end up with the sex with ADAM, for fuck's sake, and got all his extra stuff in the profile, but Jake I got only a shirtless (cute, to be fair) scene, but no sex, and only the underwear picture. No CG, no nude, no extra scenes...
That probably means you haven't gotten the "good" ending with Jake, then?
Jake is extra shy, so while he's easy to start dating, he's difficult to successfully date.
Try picking choices early on that also establish yourself as shy (like not greeting people as enthusiastically when you first meet them), and be more generally understanding and patient with him while actually dating him.
(Once you achieve a "good" ending on a route, you'll unlock the full set of features in that guy's profile.)
I could have sworn I had a good ending with him. We had the scene where he asks for us to lie shirtless together, and I know thats not really a sex scene, but it was a cute way to end it. But I wanna bang him (and it would be really sexy if he got to bang me too), so I'll try being more shy next time.