OMG…it sounds just like my marriage. Exactly like it. He even tested for testesterone, but it was all normal. I struggled with it for years, tried all tricks in the book, lingerie, cute surprises, erotic movies, porn, conversations, what not – nothing worked. We too started out with rather “moderate” sex (and this is how you can tell what’s going to be later on). And it only got worse with time, much worse, just like with you, once a month or once every two months, he too was very passive, always expected me to initiate things, did not even like BJs (and I enjoy doing it), and the quality of the intercourse was so pitiful..ugh..you’d feel sorry for me if I describe it. lol. And this is with a young, handsome, fit guy. I am a very attractive woman in a great shape, men and women tell me that and I know that myself.
Everything else was fantastic, he told me he loved me and he certainly acted this way (and I did feel it, genuinely) in all other ways – except sex.
I know you are not going to like it, but I advise you to walk away now, especially given that you are young (you said you were a virgin before him, so I assume you are young). You’ve already spent 4 years on this guy, IT WILL NOT GET BETTER, you are in denial, and with time, you would accumulate so much resentment against him that it would cause you emotional issues and would lead to something that can potentially cause serious problems if you are married to him (you having an affair, emotional stress, divorce and what if you have kids, they would lose their father, financial complications, etc etc).
Sex and intimacy is a very important part of our lives, and we live only once in this shape and form, so think about yourself and your needs – walk away now. Do not marry him, even if he is a saint and treats you like a princess. Unless, of course, he is ok with you having a permanent boyfriend for sex. lol. But would YOU like it? Most women would prefer to have a normal sex life with their husbands, especially if everything else is good in their life together.