Partner w/o BPD is also seeking help and I don’t know how to cope

I bought my boyfriend the book “How to Stop Walking on Eggshells” and it handles understanding and living with someone who has BPD. He’s been putting a lot of time into it and he says it has helped him a lot but lately it feels like he’s a lot more hurtful and just plain mean to me sometimes. Idk if this is me being overly sensitive because any type of push back feels like the worst rejection or if maybe it’s just him finally setting boundaries and standing up to my moody ass. 

I took a peek at his reddit profile the other day (we shared usernames when we started dating so it’s kosher) and he’s started going to a subreddit about loved ones of those with BPD and has partaken in venting on a few occasions. I read the things he said and they were really hurtful and they genuinely make me feel terrible and sad. I don’t know how to handle it but I understand that he needs a support group too. It just feels like that particular subreddit is mostly negative and most people there advocate for you to leave your BPD partner. 

This whole experience is just tripping me out and I don’t know how to handle it on my own. Please, I desperately need advice if anyone has any. I want to cheer him on but it feels like he’s going to leave.