How do I handle my controlling daughter?

My daughter can be very controlling...it's her way or the highway sometimes. In some sense, she is immature (and possibly spoiled), even though she is 26 y/o. She lives with her boyfriend far from home, but she's on my case often about what I eat and who I date. I am a widow so maybe that has something to do with it.
I'm sort of at my wits end. After dating the same man for several years, she has made it clear she really dislikes him and can't see what I see in him. I realize he doesn't have a lot of money (and I'm financially very settled) and that he has had financial issues in the past, but he seems to have recovered and I've know him and his family for many years so he's not some kook out there. Whenever he tries reaching out to her, she freaks and she also freaks when she hears I'm with him. To be transparent, he did get "into trouble" many years ago for a financial matter, and maybe she's ashamed if I'm with him?
She yells and hangs up the phone on me when his name comes up.
I'm happy with him and he has been very good to me and my son. He wants to be part of my family and me be a part of his. I may want to live with him (he already wants to live with me) and I'm not stupid and realize I need to do some legal work to protect my finances.
Other than avoiding his name, I feel that I just need to tell her to back off (nicely but firmly). This is my life not hers and I'm very hurt and disappointed that she is behaving this way.
Does anyone have any other thoughts?