That's such a hard situation! Especially because you've dated him for so long - probably hoping that your feelings would change with time, but now you've just gotten closer...
In my opinion, if you've dated him for a few months and are still not attracted to him, I don't think it's probable that you will become. However, I do know that it does happen that a person can suddenly become attracted to someone after they've known them for a while. Something usually happens (could be something really small) and things just click.
I find that happens in two situations (from personal experience): 1. you didn't know the person (or all sides of them) and then you see something/a part in him and you just start liking him, or 2. You may not be infatuated with him (ever!) but by getting to know and truly appreciate this person you will start to love them. You will enjoy being married (physical) to such a person and it is a different and much deeper kind of feeling than infatuation. Infatuation is all-consuming. It's a very powerful thing that you can build upon and turn to love. I have never been infatuated with someone and then gotten close enough to them for there to be love, so I can't say how it feels different from just plain love to someone you weren't initially attracted to.
On the other hand, if you've dated him seriously for months, and you still aren't attracted to him, then you should ask yourself if you think you would enjoy being physical with him. If the answer is no, then I don't know what to tell you except if I were in that situation I would probably not think it's a good idea to get married. Trust me, he won't want a wife who doesn't enjoy being with him, and you don't want to find yourself looking at other men...
I would ask a mentor and be very frank with him/her.
Good Luck 😕