Quote: The thing I am currently wondering is - if we are capable of wonderful, connected sex then what causes us to revert to either miserable, unconnected sex or not having sex at all. Instead of asking why don't we have sex more often? and better sex more often? I am wondering why do we have such good sex sometimes?
Maybe because your H and you don't have completely incompatible sexual philosophies but philosophies that only overlap. For instance, perhaps your H has the philosophy "Sex with my wife should be a celebration." and you have the philosophy "Sex with my husband is a cause for celebration.". For you, sex with your husband is something you need in order to be happy in your marriage. For your husband, sex with his wife is something he wants when he is happy in his marriage and with life in general. When he is unhappy he prefers to take care of his physical sexual needs himself.
It's pretty easy to see how this difference in sexual philosophy can lead to some vicious cycles. If he only wants to have sex with you when he is happy then you might be tempted to put yourself on some horrible hamster wheel of trying to make him happy so he will want to have sex with you. Also, the more you make it clear how unhappy you are with your sex life the more unhappy he becomes and the less he wants to have sex with you.
IMO, all you can do is accept, respect his philosophy but be honest about your own philosophy. For instance, you might say something like "I think that it is okay sometimes for people to seek comfort from sex they are unhappy. I might want that from you sometimes. Would that be okay? It would be okay with me if you wanted that from me even if you don't feel comfortable with offering it to me in return.".
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver