i think in real life, if in case the author is somewhat basing this on real life, it's just much more convenient to just run away from your problems than facing the drama. to be honest, it may or may not come up and catch you. so sumin's problems are just about to catch up, and she just doesnt know how to handle them, her natural way of dealing with difficult situations is to run away. so sungji is now, well, a difficult situation, and she's doing a "i cant deal" attitude.
which ends up with her past GFs just breaking up with her, and she's used to it. and that's how she deals with it. but let's see, if this is a healing story, im wondering how the healing will occur.