Sex with my partner is terrible

I need some advice as I don't know what else to do so I'm just going to go all out and explain everything.

I'm with my partner 9 years. Sex has never really been great. He is a big man with a small penis so finding a position that worked was just me in top. Instead, he focused on foreplay and then done-its over! That seems to be our sex life. Maybe once a month but can go longer. I've looked back on my calender and we have only had intercourse once this whole year. He needs viagra but won't get it. I have had multiple conversations over the years about this topic but nothing has changed. Last night I brought the subject up again asking if he is interested at all in having sex, not then l, but in general. He replied he's tired. He then stop speaking altogether and went to sleep and then this morning didn't speak to me.

I really don't know what else to do. I am really struggling with frustration particularly around ovulation and I've no real interest in doing it myself. I don't put any pressure on him and never make him feel in any way inadequate. How can I approach this in another, respectful way?