You're def in a rough spot. I didn't mean to imply that he didn't care about or having feelings for you, but he's still number 1 in his world. I've NEVER even thought about asking to have my penis touched while in a 3some. I thought I was blessed simply by being IN a 3some. Ya know?
Relationships don't have expiration dates on them, but they can expire. Something to think about.
Unless he changes, I can't see where you're going to be happy with the sexual side of this relationship. His gf has put up with it for 6 years and in doing that she's spoiled him into thinking that's how all women are going to act. Some may be content, but my guess is that you'll get fed up sooner rather than later. That's not to imply that you're a quitter or going to give up easily. I'm just saying that if this is a problem now, it's only going to continue to grow, again, unless he does something about it.
Live life to the fullest 'cause you never know if you're gonna wake up tomorrow!