Concern for my sister gone wrong

Since she is 6 years younger and having an alcoholic mother I have a different type of bond with my sister. I gave her baths at night, picked her up from middle and high school, and looked after her as best I could being that young. Now we are ‘all grows up.’ She’s almost 32. I know she wants marriage and things like that but her boyfriend has yet to propose. It’s been about 3 years which is not ‘that’ long. However his situation is tough on her.

His dad has a long battle with cancer and needs round the clock care. My sister has been supportive every step of the way. I know it’s hard on her. The situation is very draining emotionally on her bf and spills onto her. I know she wants her bf to propose. He knows too but he doesn’t. He took her to a ring store once but never got her a ring or proposed. Kind of like dangling the carrot or something. He is now house hunting. For himself. I want to scream about it- just not ok and selfish imo.

My mom kisses his ass. I told her my red flags with him and all the time and energy and loyalty my sister has displayed with nothing in return from him that she wants. So then my mom betrayed me and made me sound really bad in text messages. She told my sister I can’t stand her boyfriend and that he makes my skin crawl and I don’t ever want to associate with them. My sister took it straight up and has blocked me. There is no way for me to contact her. I am genuinely concerned but made out to be some evil sister. I’m pissed at what my mom did but the damage is done. I’m the only one with my gut knowing she is not in a good situation but have been shunned away. :(

Just sucks... thanks for the vent. Hopefully I am wrong and they will live happily ever after. But... I’m not allowed to be concerned about my sister that is apparently not ok? 😔