I feel like there is more your DH isn't telling you. I wouldnt really care if my DH agreed or not, I would call the police and also get an RO on the ex and her son. Keep yourself safe. I wouldn't put it past these crazies to cut a break line or something!

Stuff to the bio parent and stepparent but bio parent says no I don’t wanna report or police come and he lies it was a disagreement i won’t press charges because you know I don’t want to ruin the kids life

people need to know that there are consequences for actions, you don’t get a free pass

You live there, which means anything this kid does on your property, like trying to set something on fire, could put you in danger. I would make a police report, regardless of what your idiot husband wants.

So, not only do you have a high conflict BM to deal with, your husband still has contact with his ex GF, who has a psycho son? What fun.

Don't get me wrong, there's no rationalizing crazy if you're not also crazy - but something about this doesn't sit right.

I'd be pressing DH for more info on the crazy ex girlfriend contact. 

What did she want from him that prompted such a completely insane reaction?  

Even if the boy acted entirely on his own it sounds like the incident should, at the very least, be documented for when one or both of them escalates.

A police report doesn't mean anyone is pressing charges.  But it starts the paper trail for when you do need to take action.

You don't need DHs permission to put something like this on record although his support and cooperation would be nice.

There has to be more to this story. You have been posting here for a couple of years - so it has to been at least that long since DH broke up with this woman. Why in the world did would she contact him and why did it upset her son so much? You have said you thought SO still had a thing for BM - maybe he has had a thing for ex-girlfriend instead? You need to have a "come to Jesus" and find out exactly what is going on.

Keep the piece of paper and make a police report. Making a report does not mean you are going to press charges.

How long have you been married?  So why is there “something with the ex girlfriend.”  I’m assuming you’ve asked him this question...if not why not???

Your DH is still a slime ball.  I'm sorry but there is ZERO reason to be in contact with an ex-girlfriend.  Something is fishy and he's not telling you a huge part of the story.  No reason the ex GF's son should be mad at your DH unless he's done something to/with the ex-GF.

If it smells like b.s. and looks like b.s...

If I were cheating, I sure wouldn't have left that burned piece of paper sitting around for you to find. And I would probably have whipped up a better cover story that had NOTHING to do with my ex and ex's kid.

I don't think he's necessarily cheating. Maybe the ex contacted him and he didn't tell you -- that's lie by omission, not cheating; maybe the kid has some legit or perceived beef with him for something from the past that has nothing to do with the present...you really have little information to judge what's going on.

But it does sound potentially dangerous, so get to the bottom of it. Tell your guy you need the truth, even if it's something bad because you need to judge whether this kid is dangerous to you or your property. Be very frank, tell him you won't get mad, but you need the truth. (You can still get mad after you get the info.) If he resists, start hinting you might take bigger steps: "Well, if there's nothing more to it, this kid is obviously nuts. I'm going to just call the police to make a report so there's a record, just in case there are other problems." This is really what you should do -- call the police so they can make a record of what happened, even if you don't know who did it and other info is vague. This is helpful if there really are other incidents. However, by telling your guy you're thinking of doing this, you also spur him to spill the beans before you involve the police. You don't have to have any intention of calling police (although, as I said, you really should), but see if you can leverage the info out of him. If he's up to no good, he sure doesn't want that becoming part of a police report!