Sol, sorry about your mom I hope she feels better soon!
You know I love you so I'll drop a 2x4 on you. Don't stay over at HG's, period. You're not ready to go there and it's only a matter of time that it will happen if you end up at his place with a few extra drinks in you. Not that there's anything wrong with it between two consenting adults but you're not fully over your H yet and therefore you'll end up hurting yourself. Your H's reaction is understandable. BTW, I have no clue how he could even find out about it? Like what friend would tell on you like that? He probably knows it's HG too?
As for his reaction, I'm sure he was hurt a little once he heard about it because it was the first hit for him. You're probably thinking well why does he care if he wants the D? I wish I could answer that but I know it affects them too especially if they're not in a relationship. Some are better at hiding or reasoning with it than others. However, this will help him ease his own guilt. He's going to make this a big deal and will believe that you slept with someone just to sooth his own guilty conscience. I do believe all these WASs have bouts where they feel they made a mistake, the more you go dark on them, the more they feel it so that's one reason for why he says all these things. You can't just be with someone for so long and so intimately to just go on without thinking about it. Of course, they're quick to replace those thoughts with how bad things were and why it was still a good decision blah blah. The other reason is what wii mentioned i.e. to manipulate you for his benefit, we all know he's done that before too.
So I'll ask the same question as I have before- what do you want? Do you want H? If yes (to me it's obvious but I don't know if you've thought about it like whether you can trust him again or start a family with him etc) then he needs to know there will be no 'us' after D and that you'll probably move out of town too. So he needs to pick one or the other. If you don't want him tell him you don't want any more discussions about 'us'. He made his choice and now you've made yours too so let's get the D done and go on our merry way.
Focus on school, have platonic fun with with HG. Hang out with other friends, life's full of fun and exciting things. Take this time to enjoy some of them because sooner or later you'll be in a serious relationship and probably start a family. Enjoy your freedom while you have it
Me: 35|WAW: 38|D: 6yo | http://tinyurl.com/2dxx7m6 Feb 2006, left, came back in two weeks Aug 2006, left again Apr 2007, filed for divorce Dec 2007, reunited Mar 2010, moved out, filed again