I definitely understand where she's coming from with all this, but I also know how much it must hurt her senpai to know that she feels that way, to basically have known it from the start but tried not to think about it until she forced the issue. And it can only hurt Tsumugi to know that senpai feels that way, too. Neither of them are really doing anything wrong, but they're both hurting the other and then getting hurt knowing that they're hurting the other and neither really has an out.
For Tsumugi to not her her senpai, she needs to give up on a core part of her worldview, one built out of a deep hurt and giving up on would feel to her like she's in some way replicating the hurt that was directed at her parents.
For her senpai to not hurt her, she needs to kill a part of her that gives her joy, something that you can tell from every part of how she's acted has given to her a feeling that she's long lacked in her life and completed her in some way.
And neither of them want the other to go through that so you can see both of them actively considering going through it themself to prevent the other from having to. In the end, someone is going to get hurt in some way.