I went back and read all of your posts here,
@MS86TO.
In many ways he sounds like a sweet guy, and it is understandable that you really care for him.
One thing that does bug me a lot about what you have written is his stubborn stance about the dollar figure. It seems like it is $800 to move in with him, take it or leave it. Sure, maybe that is fair and maybe it isn't, but it's really very concerning that he has cited that number and is sticking to it rather than listening to you.
I don't know how much of what you have written here has been communicated to him, but, it sounds like at least you have tried to suggest alternatives and he has just shot those down. This tells me that he is not negotiating in good faith, because saying "this is my only offer, no room to negotiate" is not how you should deal with someone you love. To me, that is the biggest red flag. He is not honoring your feelings or ideas about what is fair. He's a poor negotiator because he doesn't see the other person's side of the situation, and I actually think that $800 a month on a $1200 a month mortgage is a bit bullying. Other people may think it is fair, but i would argue that $400-$500 a month is more fair, because as an unmarried couple he is building equity in the home, while you are not. YMMV. But you don't want to be his tenant at all, and so he should honor that by really working especially hard to make you feel safe in this move.
Have you both taken a Myers Briggs personality test? Here is a link to that:
https://www.16personalities.com/free-personality-testI suggest this because of differences you have in decorating, the broken clock, thoughts about how to handle finances, etc. As a pair, the two of you sound a lot like my other half and me. We are madly in love, but we certainly have our different ways of going about things (INTJ with an ENFP . . . so three out of four things are different.) However, watching some videos about each other's personality types has really helped us both realize that our complementary styles actually make it fun to be together. For example, I like to travel, but I'm terrible about planning travel details. I also wait until the last minute to pack, don't know what times the trains run, etc. My other half is really good about planning tiny details, which I appreciate, but then gets upset when things don't go according to plan . . . that's where I pop in and say it's okay for us to go with the flow. We can think about the cancelled flight as a chance to have a nice dinner in a new neighborhood, or bad traffic as a chance to pull off an exit and get smoothies. Whatever. On the flip side, I'm much better about financial planning, which stresses my other half out probably due of a lifetime of baggage and insecurity around money, although that is improving as we work as a team. Are you ready to work as a team with this guy? And is he ready to work as a team with you? Or is he going to try to dictate the terms of everything, just like he is dictating this rent payment rather than compromising?
He wants to have his cake and eat it too without getting married. He wants you to pay more than half his mortgage and have all of the other benefits of having you around full time (because you sound great! please come decorate my place!)
You want to get married . . . it is clear. Then there is no "my money and your money" or "my house and you pay rent." It is just "our house." Sure, maybe it isn't the house you would pick, but you could then feel okay staying there for at least 5 years because you'd be benefiting from the gain in equity. And it really would be "our house", because you'd get half of the home value if there is a split regardless of where the down payment came from. That's how it works. If married, you could agree with his idea to stay there 5 years building equity, and then plan to look for the next house together as a couple to try to get more of the things you are looking for yourself in a home.
Have you told him that you don't feel comfortable living with someone again without getting married? Have you told him you feel like you got burned other times by moving in and giving up your own independent residence without getting married? Is he listening? Or is he dismissing your feelings and ideas as silly or not important or wrong? He should understand that you want to get married before living together. If he doesn't, then he just isn't the right guy at this time despite his other positive qualities.