Well, I think one of the important things to remember is that each relationship will develop in its own fashion, for better or worse. We are always best served by letting them find their own equilibrium, whether they end up as close attachments or not. It's when we try to force them into a mold that they are most likely to explode.
It appears from here that you're trying to force your relationship with #2 into a mold. "He should be doing ..." this, that, or the other thing. You want him to be as attracted to you as to #1 and are upset that he doesn't appear to be. That, however, is how it works out at this time. You can't force him to be more attracted to you. You can't reasonably expect him to even act like it.
What you can do is figure out exactly what you need in your relationship with #1 and discuss with him how to get that. You can discuss with #2 what you perceive and what you feel about it and then work out with him how the two of you will interact.
Keep in mind that the current state of affairs will change. As the NRE between #1 and #2 wanes, their relationship will change, and your relationship with each will also change. Ties can strengthen or weaken in any direction.
I suspect changing your expectations would be of benefit. It's not an easy thing to add a third person to a couple in any configuration. Expecting the ties to be equal all the way around is a dangerous expectation to have, as the odds of each person being equally attractive and compatible with two different people are quite small.
Indeed, you may find that merely having a friendship with #2 would prove more rewarding for both of you. That allows you to enjoy your relationship with #1 without complications from dealing with #2 at the same time. It would also allow them to build a foundation for the long-term with fewer complications. And then, maybe, after the foundations are solid, you and #2 may find that you're both on the same page and the two of you can then build a foundation.
Or you may find somebody else to complement your relationship with #1.
Relationships of any sort aren't built in an instant. They take time to develop and for those involved to decide if it will work on a long-term basis. I was involved with a GF for over a year before we parted ways, as it took that long to figure out if there was a long term future there (I love her, but no long-term compatibility).