Who is "Him" and the other? A different couple than the below?
I'm not sure what other research you've done into polyamory generally, and managing a triad specifically. Please check out our resources list here:
Triads are the hardest form of polyamory to do. There are three dyads in a triad, and the feelings and dynamics will develop at different rates. You're in NRE right now, hormones are at a fever pitch. As you continue to date them, the dynamics will change-- how you feel about each person, and how each of them feels about you. Also, you have to negotiate "couple privilege," their status as a longer-term established couple (perhaps even married) affects how you will "fit in."
It sounds like all your dates so far have been as three? I hope they are amenable to having solo dates and solo sex. Some so-called poly couples aren't, because they fear it will threaten their relationship. The sooner you find this out, the better!
Personal anecdote: I once dated a guy for a short time who had a long-term gf. He brought her along on our first date for dinner, and I liked her very much. My second date was with him alone. My third date was mostly a sex date with both of them. It actually went well. We had sex as a three, but he didn't cum because he was so busy orchestrating everything (he was a Dom). After getting dressed and chatting for a while in the living room, he indicated he wanted more sex, and his gf wasn't interested, so she gave her blessing for us to go off and do it one on one.
Finally, I had one more date with him, but he had to let me go because of issues with his kids' custody, and his ex (their mom) making his life complicated. It seemed to be going well up to that point, because the gf was chill and tolerant of the guy and me being alone together... I mean, she was his sub, so whatever he said, she was likely to agree to. It's too bad I didn't get to see where this could have gone.
I hope your couple is as chill and welcoming! Just remember they are individuals, not a Borg (Star Trek reference).