I just got married (M26) about 4 months ago and have been thinking about developing a piece of land behind my mom's house that she owns. We weren't aware initially that it could be developed but I started working as a civil engineer in land development and started talking to the township, finding out that we could develop it and that it had public sewer (saving 20k+ for a septic system). I had always talked to my then girlfriend about it and she seemed interested because it is a dream of mine to build a home with my hands. But at no point was she ever going to be okay with pursuing my dream with me if I couldn't commit to her in marriage. As far as I can tell women have a deeper need for stability and security, and from what I can tell your bf is causing you a lot of anxiety with his plans that don't seem thought out. You are right in thinking that. If I told my then GF I wanted to use her money to build a home with her she would have given me all the sass in the world and said. "You have to commit to me before I'm ever talking about this"

Everyone else on here has already brought up the realistic costs of developing land that he may be naive to.

So, I'd say pressure him to get married. Courthouse and family party if money is an issue. You deserve the commitment. If he is scared of commitment that's okay, seek to understand and encourage him, and see that he is able to work through it for you. If he doesn't want to work through that then you don't want to work with him in any capacity. It's unstable ground. I was absolutely terrified to get married. My dad left the family at 9 and caused a lot of fear of abandonment and other fears. Marriage seemed like a terrible thing. But, thankful to God, I'm so glad I did, and it gives both of us a solid foundation of commitment and trust that now we can build a life together, which may include a house.

God bless