Do you think it's better for him to stay with someone that isn't attracted to him? One day he will know. Ans then how will he feel knowing you felt that way about him?

Break up.

Just tell him "i'm not happy. I like you a lot as a person, you are truly a great person, but i can sense, feel deep down this isn't the right fit for me. I truly wish you well"

Sometimes you gotta rip it off like a bandaid and just do it. Won't be the last time in your life you have to go about something this way. Otherwise you're just wasting yours and his time.