Based on the information provided, I’m making the following assumptions:
You love & respect this man
This man loves & respects you
You love and respect his child
He loves and respects your child
You love and respect your child
He loves and respects his child
In a nut shell, you are in a good relationship that is healthy for both you and your son.
If these assumptions are true and you decided to leave only because you want to have another child this could be confusing and damaging to your child. From your existing child’s and boyfriend’s perspective they could feel that this unborn child is more important to you than a happy stable home (or more important than they are). Even if you don’t agree with this statement, you should look at it from the others perspective and ask yourself…is it?
That being said, if you decide to stay, you do have to come to terms with not having another child. You need your boyfriend to understand that this is a difficult thing for you to grapple with and from your perspective it is a loss (just like if you lost a child or a pregnancy) and should be treated as such. You will need his support and understanding. Of course you can continue to discuss if another child is a potential option or not, but the final decision should be made ASAP so you all have a clear picture of your future together.
Remember, families come in all sizes shapes and types.
I hope this isn’t offensive and that it is helpful. Whenever I’m faced with something that appears to be insurmountable I remind myself of the quote below. I don’t know where I heard it, but I like it and I see it as a positive reminder that I can deal with anything given the love and support from myself and others
“Worse things have happened to better people – and they survived”