You have gotten some great responses. I agree with Kindeyes that this might be a natural hesitation for both of you to protect yourselves. Be patient and just keeping going to see him. You just both need to reconnect and have faith that you will do whatever it takes to be together. I also agree that I would just let the past go and not allow them that power over you. You can have an honest conversation with your son at some point but for you now, I think it's important to just show him who you are and let him "see" for himself what you are all about. (((HUGS))) I know you are in a tough position. Yesterday was just the first day.
I also wanted to chime in about what peaceteach said. When I had my boys, I felt NO connection to them whatsoever. I don't think I even felt like their mother until they were about 6 months old. I had an alcoholic husband who was gone a lot and two colicky/reflux babies. It was H*LL. I told XH that I felt like I was caring for them out of a sense of duty NOT out of love. It took me a LONG time to fall in love with them. Now they are my world and my joy. You will fall in love with your son again. Your brain is just trying to protect you right now.