Boyfriend's Significant Other is overwhelming

Hello! first time caller long time listener ,

I am in an ENM relationship with a super great boyfriend. I also have a SO. My boyfriend has a SO too, who is really nice and has been super supportive of our relationship. My SO established from the beginning that he wasn't interested in developing a relationship with my boyfriend or his SO, although my SO is supportive they don't hang out with or socialize with the three of us. At the beginning of my relationship my boyfriend, his SO and I worked to cultivate a friendship amongst the three of us. A lot of this had to do with my boyfriend's SO really wanting (and needing) all of us to be cool with each other, particularly as neither my boyfriend or his SO has ever been in an ENM relationship before. Even though the SO wasn't exactly the kind of person I would have gravitated towards naturally--I wanted to give it a shot. I have a really rich life full of friends from school, friends from work, friends from my hometown etc. School and work keeps me really busy so its often hard for me to see my boyfriend more than once a week. This leaves even less time to hang out with my boyfriend and his SO.

I got the sense early in my relationship with my boyfriend that his SO was looking to develop a close friendship with me, and because of time constraints and life constraints I didn't exactly have capacity for that, but I did my best to get to know him. My boyfriend's SO is a really nice person but he has experienced a lot of trauma in his life; he often brings a lot of that trauma to our interactions so hanging out with him often consists of him overloading me with his problems and challenges. He often talks down to himself in my presence; about his body or his clothes. And sometimes when he complements me he adds something at the end of the complement that is negative about himself. My boyfriend's SO is constantly texting me, so many times a day, either just one on one, or in a group chat with my boyfriend. He also sends me tons of DMs on socials, again one on one or with my boyfriend too. He is really sarcastic and very online and super into pop culture and celebrities so I don't always understand what he's posting about when he sends me memes and such. And all of this is a LOT of communication...like a hundred texts and messages a day...

A few months ago this got to be a lot, particularly as my boyfriends SO kept making me feel bad about not having time to hang out and pressuring me to do it--but also making me feel guilty about it? He would say things like "I know that you are busy and important, but I miss you, when are we hanging out?" The reality of this was I realized I was spending more time texting with and seeing my boyfriend's SO more than any other friends already! I tried to gently but firmly set boundaries, which was particularly important as this was happening during a time when school was intense for me. Setting boundaries was really hard--I tried to help him understand that it was great getting to know him, but that receiving so many texts that I couldn't possibly answer was feeling overwhelming. I also told him that I don't often know about the things he was texting me or messaging me about, or that I didn't know how they related to our friendship. He said he understood my boundaries but he also cried during the conversation, and said that he had been really hurt by friends in the past. I told my boyfriend about this conversation. I don't think he was happy about the situation, and think he was disappointed to hear that his SO didn't seem satisfied with our friendship. But he respected my boundaries and said that he would help me hold them, and that he would talk to his SO.

For a while my BFs SO was respecting my boundaries, but then he started creeping back into the same kind of communication and interactions that I asked him not to say and do. He's also having some major trauma with his family so a lot of his texts are about that, or Harry Styles (who I don't even like) I told him recently that school was really busy for me right now but he doesn't seem to even remember that, and just keeps texting me stuff that either doesn't matter to me at all, I don't understand, or stuff that makes me feel bad because its either about his family trauma or how I can't hang out. I'm frustrated with him again but I already had a conversation with him so I don't think he's hearing me, and i'm starting to feel resentment.

My BF and I have an awesome relationship. I feel like at this point I've really tried to be friends with his SO but I think we are very different, and have different interests and perspectives, and that I don't really jell with him--although I'm likable and friendly--and that I've really tried!

I feel like I should either have another conversation with him, or maybe just stop answering his messages or responding to him so frequently without saying anything?

I care about my BFs SO and I tried to be their friend but it doesn't really feel like its working out--but I don't know how to say that without hurting him.

I don't feel like my boyfriend and I's relationship hinges on my BF's SO and I being friends, but it does make it easier.

What do you guys think? Thanks so much!