In that initial moment you were blindsided with hurt, did you want to hurt your H back by way of your son?
You should ask yourself the question why you did it and then say sorry and explain in appropriate language your reasoning if you can to your son.
Kids forgive parents for messing up they do, but you need to say sorry and give an explanation. Or just "sorry baby mum lost her mind yesterday with a big shock". And let your son respond, ask questions, talk. Just listen to him.
As for you and H, keep everything else going forward between just you guys.
Own your mistake, don't use your son as a counsellor or ally against H. Move forward calmly. If your son asks questions like "does H love someone else" the real answer, unless you know otherwise is "I don't know" H might have liked the danger, excitement, but do you know he actually loves OW?
It sounds like this is could be a shit storm. There is another whole family involved and it sounds like you sort of know them.
You need to find your cool OP.
Eventually it will be ok. Remember that.
Find a sister/friend whom you can sound off to this evening if you can you need to get a lot out of your system first before you can think and act calmly.
Many kids see, live through much worse than mum losing it once. You might not be able to see the bigger perspective but they do. It will be ok.