OP, it is absolutely a valid reason to end a relationship IMO.
It is a bit different if a partner doesn't want it, but wants to start 'wanting it' again, if you get me. Or realises the the other person feels rejected and doesn't feel the situation is acceptable. Surely then any loving, caring person would want to change or get help?
If you are saying that your DW iS such a fantastic woman in every way and she loves you, then surely she can see that you are unhappy.
Now either you are not making yourself crystal clear with your DW OR she is a selfish woman who knows that you will put up with whatever she says or does. In which case you haven't really got a wonderful relationship. Either that, or she does like sex but not with you.
Sorry to sound harsh, but I am always totally amazed at these type of threads where the op says 'oh apart from this everything is great'. A sexless or almost sexless marriage is only great if that is what you both want.
Another thing that always confuses me is when it is mentioned that actually the other persons libido was never good and that in fact, you were never sexually compatitable from the start. Well, hello! It is not suddenly going to be fantastic. Do alarm bells not ring. It seems some people just allow themselves to drift into long term relationships with people they are totally mismatched sexually with and then complain years down the line that their missus never gives em a blow job(when she never did from day one0.
I haven't read all of this thread OP, but what exactly have you said to your DW?