I think the main thing that keeps me in this relationship is I want my son to grow up in a home with both of his biological parents still together.
That's fine that you want that. But if the other parent does not want the same relationship model as you, then you cannot "be together" romantically. Does not match.
Be Open to being together as friends and coparents though. You can come together on those tiers. Rather than friends, coparents AND live-in lovers. You are also teaching your kid how to behave in that situation well in case the kid grows up and faces same.
I don't know what staying in a dead relationship proves. My MIL stayed in it til my spouse (the youngest) graduated HS and they STILL go at it hammer and tongs. None of the adult children was surprised when the divorce finally came down. Just robbed them all of quieter/more peaceful childhoods because the parents are still argue-y to this day
. Had they split sooner maybe some of the kids would have had a calmer home environment and the arguments shifted to "only when we have to deal in court days" rather than daily ugh. Because they carry on so decades later? The adult children's lives are still tinged with UGH because the two parents can't manage to be in the same room together long enough to share in their family stuff -- bdays, weddings, grandkid graduations, etc. It's a pain the ass, frankly. Sigh.
I know a divorced family where the wife remarried and she and the new hubby live next door. They all continue to care for their common children even though the wife has moved on to have a second family also. That's an example from the good side of a split. They are friends and coparents. Just not married lovers any more.
Children are always watching.
Be mindful of the unspoken lesson you teach when you stay with someone just "not to break up because we have kids" or "just not to be alone."
It teaches children that it is OK to ignore their own happiness at best or makes them easy targets for abusers on the other end. Because they never speak up about their needs not being met or about enduring bad treatment at home because they are too scared to be alone.