Parenting.
The curiousity about sex is normal. AND the MORE you talk to him about it the MORE COMFORTABLE the both of you will become with the topic. I strongly encourage you to undertake these conversations yourself and not turn it over to someone else.
I would be hypervigilant about the fire starting. This can be a very serious symptom for some children.
Thank goodness you are keeping an eye on all this.
God bless,
Lois

Amber,
Hi. My name is Christina and I am new, kinda been looking around and getting a feel for things here at OH. I saw your post and just want to give you some encouragment. My son is 14 and ADHD/ODD/Biploar.(No idea what order that all goes in) He used to be obsessed with fire. He set my back yard on fire before and last summer he set a fire, thought he put it out and ended up burning up someone's fence and part of their garage. They came to my house very upset and approached my son before I even knew about it. He had my son so scared. I made him look at pictures of people who had been burned and just tried to explain to him what could have happened. He saw a house in our neighborhood that was burned down and I explained to him how those people lost everything the had. He has gotten better about fire. Most people will say the sex part is just a part of him being a teenage boy who is curious. I do like to take a drive with just the two of us, he has no choice but to hear me, even if he does not respond. With him, I have truly learned to just take it as it comes, deal with it the best I can and move on to the next issue. When things are going well, he is a wonderful kid and sweet as can be so I just roll with it as it comes. Just be encouraged and remember God knows, even when no one else does.
Take care!
Christina