I doubt if your loss of sexual desire has anything to do with your age and I also think it is unlikely that you are menopausal. Your sexual appetite can certainly diminish if the opportunities for sex only arise once every six months. Furthermore a pressure can develop within the relationship to ensure that opportunities for sex are not wasted when your partner returns home every six months. Without being facetious your sexual encounters oscillate between a feast and a famine. I hesitate to jump in and give you advice about what you should do because I am not clear if you are simply seeking clarification on what could be happening to you or are you actually thinking of getting help. It is potentially unhelpful for doctors and counsellors to offer therapeutic solutions when none are sought. Perhaps clarification is all that you require?