@misao We kinda already knew about this a while ago and the FL admitted her fault in all of this. Realizing how badly she acted was a part of her character development and allowed her to improve herself and move on. It’s why I was so relieved that this wasn’t a revenge manhua. If, like in so many other manhua, this became all “hurr durr face slap”, I would be right there with you. Fortunately, this isn’t about revenge at all. This is about self improvement and character development. Another way to look at this is that the FL is going through a bit of a redemption arc. It would certainly go a long way toward why she still wants to help out her best friend.
Now, this next part is pure speculation, but another thing to consider is that this chapter may be a case of unreliable narrator. Maybe things did happen exactly this way, but some details may have been tweaked or left out. Again, pure speculation, but from what I’ve seen of the ex, internal thoughts included, I wouldn’t put it past him. In all likelihood, this is a Rashomon situation and they were both equally at fault for the relationship breaking apart.