Co parent just won’t “Co parent”

I’m writing this because I know I’m not the only one that has dealt with this kind of behavior so I’m really hoping for some advice. I have a 2 year old son. His dad and I went to college together and started a sexual relationship. I never had any feelings or ever wanted our relationship to go any further than that. He on the other hand I believe fell in love. When I got pregnant I knew we would be toxic together so I decided to strictly co-parent with him and raise our son in a healthy environment. That was almost three years ago. We have not had sex, or attempted any other form of contact besides strictly co parenting due to me trying to maintain a strictly platonic relationship between us. Here’s the problem: he still hasn’t understood the concept of we will never have a sexual relationship again. I have to watch what I say, or do all the time because if not he thinks that he still has a chance with me. I’ve said it over 100 times, I’m really reserved and short with conversation around him, and he still doesn’t get it. It’s gotten to the point of me not even wanting to be around him. I just want to have a healthy co-parenting environment for my son where both of his parents have moved on from each other and can respect each other’s boundaries. Is this asking too much?😔