Mishka, I have just recently ended a relationship of 6 years. During the last 12-18 months, we had had no sex at all. During the previous years, it had reduced rapidly from the moment we started liviing together, no more than 4-6 times a year (previously it had been at least frequent). We are still living together - still sleeping in the same bed, since it makes no difference - but are separated. As it happens, I am now in the start of a r/l BDSM relationship.
I have been through many, many negative feelings because of this: why doesn't he want to, what's wrong with me, I must be so unattractive, I must be doing it wrong, etc etc. Eventually I realised - having tried many times to talk to him and coax him and seduce him and cajole him and tease him, you name it, including trying to get him to go to counselling with me - that it wasn't me. I wanted sex, I was open and willing to talk and to try to change and learn so as to please him. He just would not open up. I did not discuss it generally because it was after all private between the two of us, but in the end I was so desperate, I had to talk to someone A dear friend of mine just snorted and said "Oh come on - life's too short!"
It takes two: you cannot do all the running; you have the right to be fulfilled and happy. So does he, of course: but you both also have responsibility for yourselves and for your own lives. You are making an effort to improve it: he is not. That is not your fault!
No-one can tell you what you should or shouldn't do. I know what my choice was eventually, but that is not to say that is the right path for you. I really hope you manage to solve it and find happiness and fulfilment, one way or another.