Decision debt about having a baby on my own

I am 43. Through most of my 30s and now early 40s I’ve struggled with being single (after a divorce at age 30), and felt angst about running out of time to have children. Now I’m on the very edge of it even being a potential option. I am in a relationship with a man who already has 2 sons who are 16 and 22 and does not want more kids. I am buffering (with drinking) often about the decision of either staying with him and not fulfilling a desire to raise a child or leaving him and either trying a sperm donor or adopting. Sometimes I wonder if I really want to have a child and then I wonder if I’m just justifying it so I don’t have to leave my boyfriend. I’ve thought about trying to have my own child and stay in the relationship (just know we have different want matches around children) but I think that would be logistically difficult and I doubt he’d be up for that. What is one step I can take toward believing in my own wants and being confident enough to make decision?
Thank you!