That story about the cemetery plot tells so very much. I think it's very common when a spouse dies for the surviving spouse to buy two plots. It is way, way less common (unusual actually) for a parent to buy an additional plot for a healthy child. To give your mom some credit where credit is due, keep in mind that you are 36 years old. When a child is still single at that age, there is a very large chance that it is a permanent condition. So, I can see where your mom thought she was doing a loving thing.

On the other hand, everything you say about this being your mom signaling that she expects you to be tied to her forever is absolutely true. My grandmother did this exact same thing for an uncle of mine who could never emancipate himself from her. She liked keeping him completely dependent on her. Then, when she died, he became a skid row alcoholic. Thankfully, you sound way more healthy psychologically than that. For you there is real hope that you can make your own way in life. One thing you need to let go of is the financial dependence on your mother. It would be healthier for you to go live in a homeless shelter than stay forever under the same roof with her. But I think you have enough on the ball to come up with a less extreme solution.

You don't have to argue with your mother on the grave issue. Someday she will give you the deed to that little plot of land. After she is gone, you can sell it back to the cemetery. Hopefully, she won't have the audacity to go engraving your name on the tombstone ahead of time. It would be normal for her to put her own name there ahead of time . . . but not yours.

Getting that plot reserved for you was something she meant as an act of love, but it is totally inappropriate and it's a good sign that you see it as such. Maybe it will motivate you as well. You know it's not so easy to find a partner in life. If you still have feelings for this woman that you met, you might want to decide to make another pitch for that relationship. She sounds like an unusually understanding lady.

In any case, if you don't want some future nice lady to be completely scared away, then start setting the appropriate boundaries (like with the mail) and start separating from your mom. She will try to emotionally blackmail you, which is what she has done. If you cave in, waiting for a time when it won't seem so hard, you'll be waiting forever. Your mom is still fairly young and sounds reasonably healthy, so you can't just wait for her to pass away. That might not be for 30 years. Start now. I've known others in your situation. As they got older, they just became more and more resentful of being tied to a parent. Also, start now, while your mom is still in good shape and can fend for herself, if she has to. She needs to find a small apartment for herself. And so do you. I'm not opposed to adult children and a parent living together, but in your case it simply will not work.