I'm currently writing this novel, which mostly centers around a thirteen year girl with a complicated relationship with her parents. Your average 11-16 year old kind of book I suppose. But I've recently decided to extend on another relationship she has with someone just slightly older. He's a sort of aquaintance at first, in a relationship with another male, but he has homophobic parents. He talks the main character through a difficult time and she later pretends to be his girlfriend in front of his parents. However, it turns out that he has some genuine feelings for her and reveals he believes he is actually bisexual not gay. I've had various idea's about how their relationship escalates, but I'm wondering how far I can actually take the physical side of their relationship. Whether I could have it getting to the extent of them sleeping together or whether it should stop at a little touchy feely stuff. Bearing in mind that this is ideally a book for 11-16 year olds and at this point in the story the main character is no older than 14.
Oh, I should probably mention, when I say he is slightly older I mean a matter of months, he is in her tutorial group at school in the year above her, making him no older than 15. They know each other relatively well. I know I said that the main character is 13 and later 14, I have a vague idea that she passes a birthday during the story.
I think you should be extremely careful of taking any physical contact to far, given the age of your protagonist and target audience. If you are trying to portray the dangers of that type of relationship, that may be tolerated in showing a bit more.