I can so relate. I have a 4 1/2 year old son, and also recently entered the dating world. Recently engaged, so be encouraged!
I had all the same concerns as you, and my son has also recently, out of nowhere, started crying for me not to go to work (NEVER did this before.) He stays with my mom (who lives next door, so they are very close) when I work, and he LOVES to be there. But recently, he doesn't want me to go to work, wants me to take him with me, etc. It's tough because I'd love to stay home with him but can't financially.
Anyhow, as for the dating, I'd say that if you feel your guy is truly a GOOD guy, and we know deep down whether they are or not, then it's ok to continue to allow your son to be a part of your relationship. In reality, you son IS there. He is your life. So to try to disconnect him from this part of your life with your BF would not only send him a bad message (that you're choosing someone over him), but will also set an unreal precedent for what your relationship would be like in the long term with your BF. You do have a child, and much, if not most of your life will be centered around your child. BF needs to be ok with this, so why pretend like it will be any other way? And to try to keep things separate might also increase your sons obvious anxiety about you leaving him.
We did go out alone on (rare) occasions, but usually, my son was with us. My fiance knew when he decided to pursue me that my son was first, and he has never tried to exclude him from anything we do. And like you said, we usually plan the things we do around things we ALL enjoy. And for us, that has fostered the development of a positive foundation for their relationship. My son has never felt that I pushed him aside for my fiance. And my fiance has never made my son feel like he wasn't a part of our family.
I understand that there is a degree of protection that we need to provide to our children from fleeting people in our lives. So in that way, there is kind of a fine line you have to walk between exposing them to too many suitors, and allowing them to continue feel like they are a priority, not pushed aside for the flavor of the week. :) I think it comes down to your intuition. You need to trust your instincts about your guy. Realsitically, (and being real with yourself is paramount), do you see this guy long term? If so, keep doing what your doing.
Best wishes to you. I know where you are. It's tough, but you and your son will be fine!!!