You live with the boyfriend and he's acting as Dad for your little boy?
It sounds like you thought you had almost the perfect situation for a while there. As long as the boyfriend was dating others too, and not feeling jealous, everything was wonderful...
Now, though, you have to figure out what you need, what you really want, and what you can live without, because I foresee this getting thornier before it gets better.
Seriously. Figure out what you need. Not, what the boyfriend needs, because that's his job to figure out.
Figure out what you need and ask for it.
This may mean you have to ditch the idea of being a nice good girl. If you don't know what I mean by this, it may not make sense yet. In our society, women are often brought up to defer to everyone else's wishes/desires/wants before even considering what they themselves might need. You have the right to run your life. You will be happier if you admit that there are things that you need to have to make you happy. You are an adult, and you can ask for these things. You may not get them from the people that you ask. Determine whether you can live with that, or if you need to move on.
That paragraph? Written from the perspective of a recovering nice good girl. That's me. It took me ages(I'm 43) to realize that I did not have to put everyone else's feelings above mine.
I'm not advocating being rude, here, but, this jealousy problem that your boyfriend has? His problem. You are not causing it. There are lots of people who could handle the situation you describe just fine without getting insecure about the sex. His problem. You can do what you can to reassure him, but, whether or not you are successful is not in your control. This is his head, and he let's in the reassurances he wants...or not. You can point him at things to read to help him. Whether he reads or understands is not in your control. You can't do it. He is the only one who can.
Boundaries are fine and wonderful things, and you aren't being mean if you stand up for yourself. If he asks how he compares in bed, you don't have to tell him anything. That's between your Lover and yourself. If he presses, you can tell him that you don't talk to your Lover about him, so you aren't going to talk to him about your Lover.
The "when you're home alone" one is for your boyfriend.