Hi! I need some advice and even just a place to vent. 

My best friend of 15+ years deals with a lot of mental health issues. She’s previously disclosed to me that she gets very anxious texting people back. It was common in our relationship that I wouldn’t hear from her for a week or so and we had an understanding that I’d keep sending her messages when I’m thinking of her, memes, funny stories, etc. without the expectation for her to respond to each one. 
About a year ago I noticed the time in between her texts getting longer and longer but knew she was going through some stuff with the pandemic - her biggest red flag that something is wrong is when she doesn’t text back. 
Now, this current streak is the longest I’ve ever not heard from her… It’s been over 8 months. Throughout this time I’ve text her between a few times per week to a few times a month, however, after a couple months I was getting worried and reached out to our other friends to see if they’d heard from her. I found out they hadn’t and they were also worried so I reached out to her sister who confirmed she was going through a rough time and was distant with everyone. I reached out to her sister again, who seems to be her biggest support, and her sister told me that she (my friend) feels very guilty for not responding and has said she doesn’t deserve to have friends like us. This breaks my heart. I also recently reached out to my friends long time partner to check in and he seemed very oblivious and unhelpful which makes me worried about the role he plays in her health. 

I’m currently seven months pregnant. I’ve been sending my friend texts and updates but I’m getting discouraged and honestly feeling hurt that I haven’t heard from her. She knew I had a miscarriage last year and that this journey has been difficult for me. As much as I empathize with her, I feel bitter and abandon that she hasn’t been there for me. Part of me wants to keep supporting and reaching out to her but another part of me thinks I should just give up after all this time and focus my energy into friendships that are more equal…

What should I do?