I know that we are only 2 episodes into this drama, but this issue has been bothering me.

One part of me thinks that it is right that Yeondu can break off the relationship like that. As Ryu Seol said, you don't need a reason to break up with someone (or that's I remember she said it). Yeondu and Hyunho have had 2 breakups now and have been dating for about 3 years, so maybe she was tired of the relationship because there were so many conflicts (I guess we'd have to wait to see more of their relationship flashbacks as the drama goes on to see what really went on with the flashbacks we have seen thus far)

On the other hand, I am seeing it as the fact that Yeondu and Hyunho barely changing at all and this love triangle and ex-lover wanting their ex back is going to make things even more problematic than they need to be already. Maybe I am judging too soon, but literally, they could focus their time on creating some narrative on the characters rather than directing the attention away and focusing on a meaningless love triangle and instead make the two actually learn from their mistakes and communicate one-to-one and heart-to-heart, rather the two do dodging the issue.

Again, I am judging too soon, but is it really okay to break with someone without properly talking to them about how you feel, how they feel, what went wrong, etc? Is it okay to really do that when you are breaking up with someone, in general?

What does everyone think?

I think you answered your own question. Its too soon to pass judgement on the characters when we don't really know what went down yet.

As for the  writing.. Yea I think its fair to already cast some judgement lol. As much as I enjoy this show there are definitely things they could do better. So far the premise just seems like a slightly different season 2. The jealousy angle is so overplayed and boring

Yes, I can agree as well that the  jealousy aspect of things is really just aggravating at this point, as well as the love-triangles

But the rating of show has gone up from here, so that is interesting