Schedule it and ask everyone to come to the table with issues they feel need to be discussed, listen, don't just hear, allow people to say all they want to say and not but in. Don't accuse and don't respond to accusations by being defensive. Use non aggressive language.
Most of all I would say please try to imagine how your other partner and your metamour feels in the midst of all this NRE and all this NRE language, it might seem a long time ago now but I am sure you both had such passionate and loving feelings at the beginning of your other relationships too.
One day H will be the kind of partner you can take for granted as well....that is, if you are lucky and get past this point of temporary insanity (I wish someone explained NRE well enough for me to realise I would act like a crazy person and nearly ruin my life by making some truly bad decisions and stop me).
Just keep talking and not about the future but about the here and now and how you want everyone in the configuration to benefit from this relationship rather than feeling they have lost out.