Meeting You - no breakup, no love triangle, both leads basically are already best friend since childhood and quickly acts like a couple very early on and stays that way until the end.
Unforgettable Love - there's break up for a little bit but honestly the whole thing is very chill and relaxing imo because of the kid, even more so than the other titles I mention after this.
Perfect and Casual - no breakup, just wholesome relationship. Low stress.
Falling into Your Smile - no breakup and story about esports. Covers problems related to esports, not that stressful.
My Heroic Husband - no breakup, both leads loyal to each other until the end, starts as arranged marriage. Love rivals though can be a source of stress.
Reset - Slight romance, no breakup because they only become a couple in the end. Imo it's just a must watch.
Moonlight - no breakup, it's about romance between editor and novel writer. 2 couples. There are annoying "villain" that can cause stress but it's not related to romance/love rivals. In my opinion though this drama is not that enjoyable, I only watch because I really like the actress.