OP, this isn’t about what you are willing to let him have. Now that you are no longer together you are both equal parents. It’s not up to you to decide what he is and isn’t allowed, it doesn’t work like that.
While you may end up as the parent with primary residency, the fact remains that he is an equal parent to you even if you have done most of the parenting up until now.
If you went to court they would likely award a minimum of two nights a week and every other weekend contact, and while that may not currently be something which is possible and may not be what he seeks, bear in mind that the courts will rule what is in the best interests of the child, without any consideration what so ever for the financial implications.
I appreciate that you have done the parenting until now, but now you are no longer together you cannot decide whether he is or isn’t allowed to have his own son overnight. The courts take a very, very dim view of that.
And there are numerous parents on here who will attest to the fact that divorce was actually what made parents of their ex’s because they had to do it or risk losing the relationship with their children. As hard as it is you’re going to have to let this one play itself out,because although you have been there to do all the parenting on your own until now,this might actually be the wakeup call he needs to parent his own child.
FWIW when me and my eXH split up I was the primary parent by far as I’d been a SAHM,he commuted for work and so DS was predominantly attached to me. Although I will state here that ex wasn’t a bad parent by any stretch but my DS’ primary attachment was to me.
The first new year we had split we were still living in the same house and he wanted to take DS to his family for new year. I had already agreed 50/50 with him and had always maintained (and still do) that DS could see either of us whenever he wanted. I didn’t ever want to be one of those parents who dictated when my own son’s father could see him.
But oh my God when I agreed to let him go away for new year all hell broke loose among some within my social circle. People saying how I should put my foot down and say no, how it wasn’t right him being away from me for so long even though the same people wouldn’t have batted an eyelid if it had been the other way around, I stuck to my guns and they went away for a week and came back and all was well. DS was ten at this point btw.
Over the years things have changed in that DS is only resident with me and sees eXH away from his home,but there are other reasons for that I won’t go into here. But ultimately had I been obstructive in the beginning it would only have made things worse in the long run.
Even now when things have been tense between ds and eXH for various reasons I have maintained that although DS can always be the one who makes the decisions (he’s sixteen now,) he needn’t burn his bridges so to speak, and that’s stood them both in good stead as DS has grown up and matured and the relationship has changed and evolved and will continue to do so as he gets older.
Ultimately they’re not children forever, but those first years are vitally important and are what set the groundwork for life-long relationships. Never under-estimate that.