How do i tell a guy i wont to have more?

help i am a complete chicken, i have met this great guy, and i really like him have had some pionate times and he is so loving and caring, i am in a loveless marriage which is at its end, he has said little things to me and i have tried but just cant get the words out, i am worried that if i say how i feel he will do a runner, (cant see it but its my own fear)