In my opinion you're not teaching sex ed, so try not to have your personal lessons overwrite the story. Each sex scene depends on the situation, the style of book and the character. And each agent and editor will also have differing opinions--there are no hard and fast rules. Get it, hard and fast.
In my books there is sex--off page. Lots of it I guess by some standards. And SLJ did mention that a condom wasn't mentioned. However in any of the five books that have gone through the editorial process, tossing in a condom was never mentioned by my brilliant editors, mostly because it would be an afterthought and not in the actual scene.
With my two latest books I did go back in copyedits and add a character picking up a wrapper because honestly, I wanted everything to be as real as possible--and who would want their parents finding that?
But the thing is, I don't think an agent or editor will turn you down for having a scene that's "too hot". Because they'll just say, Hm... maybe we could tone this down. It all depends on the book. If you have a character who acts twelve, chances are your editor is not going to let you keep sex scenes.
All of my YA is older, so they were never an issue. In fact, if any of them were toned down, I decided to do it myself for one reason or another. So I would concentrate on writing something emotionally satisfying and move on to the things that editors do care about--writing and plot.
(But I am, of course, pro sex scene)