My take on this is he would not watch if he was not interested. I think he has not made a move because he does not want to change the dynamic you have into something less than it is now.

My fiancée and I were good friends for years and we were sharing a hot tub together one night. I had been completely single for a year and was grateful just to be alone with a woman, not competing for her attention. You really have to live where I do to fully appreciate the reality of my situation, but I am sure that even people in less remote places have experienced similar emotions. I asked her if it would be okay if I sat next to her and put my arm around her. She kind of laughed at me but agreed, and within seconds of having my arm aound her she laid her on my shoulder and started touching my chest hair with her fingertips.

"Can I just try something?" She spoke so quietly that I barely heard her over the sound of the jets. As I looked down at her to ask what she intended to try, her lips moved up to mine and she met me with a kiss.

Pandemonium.

The next clear memory I have of that night, her bikini is floating in the water and she is bent over with her hands gripping the edge of the tub and her pussy so swollen that her lips parted themselves. I am standing behind her with an erection so hard it is painful, slowly stroking it and asking myself whether this is a good idea.

I called in sick to work the next morning. We made love until the late afternoon, leaving only for water and bathroom breaks. I held her for so long that I started feeling right again.

A lot happened since then to get to where we are now, but I think what is important is that we handled it cautiously and consensually out of respect for our years of close friendship. If you are unsure how to start, asking if you can 'try something' is not such a bad idea. It sounds like you have an amazing relationship and he does not want to push you into anything, so maybe you need to take him by the hand and lead him to where the new boundaries are.