Ach, I could write a book on this subject of differing desire/libidos. I was in a long mono relationship with a man (34 years, I am now 55). We broke up in '08, and I met my current gf in early '09, and we are poly. In both relationships I've had to deal with this issue... a lot. I've been on both sides of the equation, the less horny and the more horny.
But as to your specific questions and concerns:
Is is possible he is gay or bi and has not come to terms with it? You said he is effeminate. Of course, there are plenty of straight femme men, but I am just wondering...
As for how to deal currently with your higher libido, how can you feel more satisfied while still being with him? Since my libido is higher than my gf''s, I do need to masturbate to feel relief from that pressure. Of course, being poly means I can go get laid by another person, but in the last year or so, I've changed my standards of whom to date/shag, and therefore haven't had that option as often as I used to.
So... masturbating when you've got a hot partner you wish you were sexing can feel very sad. One way my gf and I deal with it is, she never minds when I have to jill off, and quite often she "helps" me to do it, by embracing me, or touching my breasts or doing various other things, with the understanding I don't touch her erogenous zones when that is going on. It's OK if I kiss her, or touch her shoulders, or hips, or belly.
I agree with the others that what you two have going on is not polyamory, since you are both afraid of the other getting emotionally entangled with others, even to the point of being jealous of each others' platonic friends. I'd suggest being brutally honest and having lots of long thinks and talks about jealousy. Reading here, searching for jealousy in the thread tags, should help you a lot. I think almost all of us have had to work through this, with varying degrees of success.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 58, living with:
miss pixi, 37, who is dating (NRE):