Loss of sexual desire has many underlying causes, starting from psychological,physical as well as hormonal. From your description it seems that you have good tuning with him. Please look for any emotional issues, work stress, depression etc as these can be silent contributors. In their absence you may think of getting your hormone profile checked, thyroid profile in particular. Sonography of pelvis is also required to rule out ovarian cysts.
Do not feel guilty about not feeling sexually excited. It may be temporary if rests of things are normal. Try to involve fully into his passion and increase the time of foreplay and after play,  which in turn increases desire.