Hearing it from a third party might not seem as threatening to her or as scary to you.
Also I knew a couple once who kept a journal. He would write his feelings in it and she would then read it and write her response to those feelings. It was easier, for them, than direct confrontation.
Maybe this is an option for you. Oh and don't feel bad about being afraid. I was so afraid to say something to my H that I put it off for 4 years. By the time the convo rolled around, I was bawling and unable to even utter the words making love or sex. We were both incredibly uncomfortable about it and now we can talk about it with ease. Amazing.
