Trying to stay strong for my baby but feel like I'm falling apart

Like the title says, I went from having friends for the first time ever in my adult life who invited me out to do stuff and even had someone I considered a best friend who called me her sister but then in June when I went on maternity leave and came back in September everything changed. My friends stopped reaching out as much eventually not reaching out at all. Asked me out once in the past 8 months. And last week the one who called me her sister and best friend called someone else her best friend. I've been fighting depression since I was in high school and this kinda made me backslide a bit and I've been isolating myself outside of work because of it. All this is happening while I'm also trying to take care of an almost 8 months old baby girl with only my almost 70 year old mother to help as the father isn't in the picture and for obvious reasons I'm not dating anyone. I don't know what to do should I confront the girl for dropping me when I was there through every heartbreak she dealt with the past few years or should I just take the loss and cut her out completely. I have no social life anymore, no one who actively checks in on me. I have no idea how to open up to anyone anymore because how can I trust they won't drop me just the same? I know this post sounds whiney and oh pity me but I just needed somewhere I could vent this all to because my mom says suck it up because Im a mom now and my friends are single so how could I expect them to stick around (she's not trying to be mean she thinks she's being helpful saying that) I just need a place I can say this and feel like maybe someone else understands what I'm feeling