How to tell someone how I really feel?

Hi I have been posting on here a lot about my boyfriend truth is we not a couple we just more than good friends shall I say. I really have feelings for this guy and it hurts I really want us to be a couple. I have had a conversation with him about where we stand and he not sure on how he feels. I have been in relationships before whereas my more than good friend has not and he is in his 40s now. I really want to open up about how I feel about him and about what I really want which is a relationship. He a good guy last year I helped him recover after his heart attack and open heart surgery and when my mum died a few years ago he was there for me. We are 2 people with autism but the love and support we have given one another is unreal and I know we would be an amazing couple if we both tried. How can I express how I truly feel without overwhelming him? I am seeing him tomorrow as we both go to circus training on Sundays and in the afternoon I will be chilling over his and I really want to open up about everything when it’s just the 2 of us.