I want another kid, gf doesn’t. How to move on?

I (33M) have a 6 year old son, I am widowed, my wife died shortly after childbirth from complications. It has been my son and I for the past 6 years, I have dated on and off, but nothing serious, until my gf.My girlfriend (31F) has a 4 year old daughter. Her ex Bf left when she found out she was pregnant and she hasn’t heard from him since. We have been dating 3 years. So I’ve been around since her daughter was one and she’s been around since my son was 3. We do live together and have both kids full time.I always imagined us having a child of our own. But my gf is adamant that she’s happy with the family we have. I genuinely love her daughter, she calls me dad, I consider her my daughter. My son calls my gf mom, and she treats him like he’s her own.I have a ring, and have been thinking about proposing for the past year, this is the only thing holding me back. This isn’t something you can compromise on.Any advise on accepting not having more kids when you want them? via /r/Parenting http://bit.ly/2Aq38hB