what should I do (sorry long post)

I'm pretty upset with my best friend. She asked earlier this week if I wanted to come out with her and her coworkers to the bar Saturday night. I said probably not because I'd just be bored(I'm pregnant) so Thursday night we were suppose to go to the gym(we made these plans Wednesday)I told her I was ready whenever she said okay she was waiting for her boyfriend to shower up. Then she texted me saying "I guess he's not going because drinking is more important.." I just said okay... and asked if she still wanted to go. She said not really because she wanted her boyfriend to take her son who was being crabby, but since he was going out she didn't want to go. Which didn't make sense because if her bf was coming with us they would of put him in the daycare at the gym anyways? So I just said okay well let me know because I'm going to go. She said just to go and she'll meet me if she feels like going. I said I was going to a different gym if she wasn't goingwith me. So I needed to know. Well she said no. Then she texted me how she was really upset with him and she was crying and whatever. So I asked if she wanted me to come over and hang out with her for a bit, and I'll just go to the gym later. Just have some girl time since we already had plans for the gym and to just be a friend and comfort her. Well she said no she just put her son to bed and she was crying. I just said okay.. well come Friday night I see her Snapchat and she's going out to the bars with her coworkers. I thought maybe she changed her Saturday plans to Friday night. Whatever. Then last night she posted on Snapchat again "ready for round 2" now I'm upset. How come you can't come to the gym with me for an hour, or hang out with me at your house, because you're mad at your boyfriend for the same thing you're always mad about. When he was just across the street at my house hanging out with my boyfriend. But you can go to the bars twice with your coworkers? She called me twice Saturday night I'm guessing to invite me(I didn't even answer) which is nice she thought about it but I'm sorry I don't want to sit and watch you and your friends get wasted, also being around 100 other drunk people since everyone's out for st paddys day. That's not fun for me. I obviously told my boyfriend and he said I should just cut her off. He said That she's being shitty when she also knows she's my only friend and she knows I don't do anything but sit at home unless I'm with my boyfriend. And that she can't hang out with me for an hour like we had planned but she can go out with her other friends. And like when she was pregnant I still hung out with her like everyday because we were each other's only good friends. But now that I'm pregnant she never wants to do anything besides go to the gym which is fine. And I get it's harder to do other stuff because she has a kid and out schedule are different. But she goes out at least every other weekend.. But can't hang out with me for an hour or whatever when we live across the street from each other so I can just walk over to her place. It's hard because she's my best friend and my only friend. But at the same time she's like not being a friend at all. And I don't know what I should do about it.