A lot of people have already written a lot of sensible things to you. I'm just going to repeat one (before I get onto some things that nobody else seems to have said yet...): I agree with everybody who says that what you have isn't polyamory. Call it swinging, call it an open relationship (although it doesn't seem all that open
to me). I have an alter ego called Mister Pedant Man
(A Super pain in the arse) who lurks around this board and who would tell you that the "amor" in polyamory means love (in several languages), not
sex. Unless you allow each other to relate emotionally with others, it ain't polyamory.
In one way, you seem to be closer to polyamory than your boyfriend because you recognise that - for you - "If it ain't got emotion, it ain't worth a fuck". But you also have issues with jealousy:
the thought of him with someone else fills me with feelings of inadequacy, rage, and helplessness
and it's you who are asking for (a period of?) monogamy now. If you ever are
going to have a polyamorous relationship, you're going to have to work on that jealousy.
OK, on to the new stuff: There's a book in German entitled "Krankheit als Weg" by Ruediger Dahlke, translated as "Disease as the Language of the Soul"
(I suppose that it's the same book, but they might be 2 books by him in the same series - the title translation isn't exact.)
I haven't read the book, but several friends have talked about it. And I gather that the basic premis is that often (not always?) physical diseases are trying to send you a message about your psychic state.
I wonder if your boyfriend's genital rash is trying to tell him (and you?) something about him
? It might be as simple as "I don't want to have sex right now" (which he tells you +/- pretty directly anyway).
[I had a girlfriend who used to get terrible genital yeast infections. Whole areas of skin would peel off her genitals, it was itchy to the point of crying-painful, and sex was out of the question until it cleared up. I sometimes think that it might have been connected with her history of incestual abuse as an adolescent. She had therapy about this later. We haven't been in close contact recently. (We live in different countries and she has made clear that she also wants emotional distance from me - in fact, I also wonder if she wanted that while we were together...)]
Another possibility that occurs to me is that your boyfriend is (subconsciously) escaping from intimacy
with you: not just physical imtimacy but emotional intimacy as well. Take the following paragraph and substitute "intimacy" for "sex", and "intimate" for "sexual" and see if it strikes a chord with you:
The problem is, he has problems with sex. It's always been difficult for us to have a sexual relationship because he doesn't initiate sex, is never dominant, and had really bad experiences with past girlfriends and was even abused by a stranger one night while a cop just watched across the street and didn't help. Since the beginning, we have had many ongoing periods of celibacy.
Please understand me: I wouldn't presume to say that this is the question... but I think that it might be helpful for you and your boyfriend to carefully consider the possibility. [I have had enough second-hand experience with therapy - and this is something I know about myself, without
going through therapy - that if your (or your boyfriend's) first reaction to the idea is: "NO!
!!!".. you ought to consider it even more seriously.]
If not... well, maybe I've just been wasting my time (and yours).
Hope you get all this sorted out!