You're asking this question from the wrong perspective.
You're asking this as if you're owed a solution to this problem.
This is your logic:
I want to date the man I like
I don't have time/childcare to date the man I like
Therefor I must introduce son to this man early on
No. You're looking at this purely from what benefits you.
And I get it, I do. Being a single mum is a huge sacrifice and so unfair. But that still doesn't mean that it was right for you to introduce your son so early on.
The logic should have been:
I want to date the man I like
In order for me to date the man I like, I need to expose my son to a new relationship and risk him getting attached to someone who isn't permanent
This is not in my sons best interest
Therefor I will not date the man I like, because I will not sacrifice my sons best interest.
And you go from there.
Just because you want something, doesn't mean your son/the world needs to make that happen for you. And while I empathise very strongly with how hard that is, I disagree that just because you want something, your son has to bare that burden.
If your situation doesn't allow you to date without exposing your child to a new partner... Then sadly your situation doesn't allow you to date. Period.
Now, I actually do believe there are other solutions. Solutions you may not like, such as only going on dates when you have proper childcare and therefor seeing your boyfriend less. But that's the reality you have to deal with. Because if you don't deal with that reality, then the burden ends up on your son.