I think that your mother is co-dependent, or maybe enmeshed with you, from what you have written here. In any case it seems it's not a healthy relationship between you and her, and it doesn't sound like it works very well for you. I think she's ok with things as they are, because she gets companionship, by always having you around, similarly she gets her feeling ha of emotional support from you, and she can tell herself that her life has a lot of purpose and meaning because she is really needed to take care of you all the time (even though in reality it's more the other way around).
I recognise this in some ways because my mother has some similarities, tending to be very overly involved in her children. On the other hand though my mother was very abusive and I've lived away from her since I was a teenager, which in some ways has made things a lot easier for me I think.
In my opinion, I think it's really important to understand that your mother will not change of her own free will. After all, she's been like this for 30 years! So trying to pursuade her that change is needed, that your expectations are reasonable, etc., or waiting for her to come around, is likely to be a fruitless and frustrating task.
On the other hand, you can be the one to change. If you put some new boundaries down, e.g. that you will be spending time with your boyfriend whenever you decide, and for however long you like, you just need to communicate this to her in a firm way, not asking her but telling her "I'll be away from this date to this date"or whatever it is. She will probably try every trick in the book to begin with - anger, guilt-tripping, suddenly developing a mystery illness, etc. But if you stick to your guns she will have no choice but to accept it in the end.
Ultimately it would probably be very healthy and good for you to move out, and be able to live your own life without constantly accounting to or appeasing your mother. And it would be good for her too - maybe she would go out and make new friends, develop new interests, once she wasn't so interested in your life 24/7.
I wish you all the best!