Hihi, new around these parts and kinda semi-skimmed a few paragraphs here and there due to tiredness, but couldn't stop reading, hehe!
Just throwing a couple thoughts from my head to the keyboard (not directly, my fingers are running interference to prevent facedesking, I promise
As for you not being an initiator... I understand that really really too much. I'm not either. But! If you can, maybe initiate a time or two with your guy? Or attempt to at least. That way he's not giving you pity sex and when you're horny you can try and get what you want! And all the guys I know LOVE it when women initiate too, it makes them feel wanted as well and they think it's hot. *snicker* Well, I guess I would too, but still...
Also... something I'm curious about and semi-wondering... understanding that your gal is the newer person in the triad, and she and your guy are in a honeymoon stage (just going over things to be sure I understand it correctly!)... and you often all have fun together... maybe on a time or two that he doesn't want sex, or you feel like withholding for any of the reasons discussed.. or whatever... maybe asking your gal to have some one on one fun with you would be an option? I think it'd have an effect as well of showing your guy that she wants you too, and will maybe remind him that you can be the chocolate as well, to steal a phrase.
That might spark a thought or two of "hey... I have TWO desirable woman here who both want me equally!" (Or rabidly, in case of hormones!
Just a few early morning, not slept yet, after work tired thoughts. Forgive the newbie!