Grandparent caregiving. Exhausted, depressed, and feeling alone. Advice?

I am sole caregiver to my 88 year old grandmother, and I am so burned out. Both of my parents passed away and I am an only child. Both of my grandma's children have passed, and I have been left with the full responsibility of her care. She has two other grandchildren (my cousins), but they do very little in the way of helping her. I cannot fault them completely for this, as she is resistant to their help, along with the only other option which is their mom (my aunt). I have had to leave work numerous times to come to her aid, take her to the hospital (for things that are not true emergencies), miss out on social experiences, holidays, etc. Only recently has she admitted to anxiety and depression. Every time there is a holiday, she has panic attacks and I have spent more time in the hospital with her on the holidays than I can count. I dread looking at the calendar. I am afraid to make plans with anyone. To go on vacation. To even have any intimate life with my husband, in fear of it being interrupted. If she calls or texts (which is multiple times daily) and I don't respond within a minute or two, she panics and questions why I didn't answer. She makes me feel guilty with statements such as, "I don't want to ruin your life...". She questions why my husband and I don't have children. I can't bring myself to tell her that she is one of the biggest reasons...I already feel like I am taking care of one. I feel like this sole responsibility was given to me and my own needs left at the curb. I have tried encouraging her on numerous times to talk to a therapist, to try an antidepressant. I just get yelled at by her for even suggesting it. She claims that she doesn't need a therapist because she can vent to me. I have been in therapy around 8 months now and her negativity throws me off my own personal growth. I have told her I am just one person, a human being, trying to do the best I can. I have many sleepless nights, fearful that the phone will ring. There was a period of time a few months ago when she called me a couple times throughout the middle of the night, almost on a daily basis, because she was having panic attacks. I became so burned out and exhausted that I was sleep deprived, not eating, and beginning to have suicidal thoughts. I am so deeply afraid of ever getting back to that mental state again. I just want my life back. I have dealt with her emotional abuse and guilt trips for as long as I can remember. And yet, she only turns to me. Finds reasons to be angry at my aunt and her other 2 grandchildren and says she doesn't want to see them. That only leaves me. My husband helps when he can, but I don't want to place this burden on him. I know one day he will have to face this difficult task with his own parents. My grandma always says to me, "These are the best years of your life, they were for me.". These are FAR from my best years. I am hopeful to live, find joy, and peace in my forties. For now, I feel isolated, stuck, guilty and exhausted. Anyone else able to relate? I love her, but have just...lost myself...in all of this. I dread calling her because all it is is listening to her complain and list every ailment and assume even the simplest of them warrants a hospital visit. It has unfortunately and heartbreakingly become a relationship, once as grandparent and grandchild, to patient and caregiver. I just want the freedom to wake up, feel confident in my day and not that my plans, hopes, dreams, etc. will be pushed aside at a moment's notice. When I have had to set boundaries or decline cancelling a plan, she asks what the plan is and says things like, "Well, that's not important." I am sick of her deciding what should hold value to me. I want to spend more time with my spouse, advance in my career, maybe get pregnant before too old to do so, but I just feel so trapped. Thanks for listening...if you have any kind wisdom or relating to share, I would appreciate it.