Caught My Friend on my Bed

A friend of mine came to my place to visit. We had been friends for years and always got on well. I have a bit of a crush on him but we've never been anything more than friends.
After a nice evening chatting and watching films, we went to bed. We agreed to share my bed since I only had one bedroom. I did find it quite a turn on stripping down to our underwear in front of each other.
In the morning, I woke up first and went to have a shower. When I finished I pushed the bedroom door which has not quite closed shut. I stepped inside and saw my friend had taken off his underwear and had pushed down the covers and was masturbating with his eyes closed. I was very turned on and watched him from the doorway for a short while before leaving him in peace.
It turns me on very much thinking about that morning and the fact that I saw him masturbating and he doesn't know I saw him.
I have thought about that day many times when I pleasured myself on that very same bed.