@RandomnessOfTheMathWorld
if you take look from manga logic, anyone would think "she must have some circumstance to make her leave Rudeus behind".
if she just want to dump Rudeus there's no need to sleep with him.(well, i'm not expert at this kind of affair)
well, the letter "Right now we're not a good match for each other" is rather misleading, anyone in Rudeus shoes would thought "i'm not enough for her".
on contrary, Eris actually think that She is the one not good enough for Rudeus