If a story makes me ask what made mc fall in love with ml, or why would ml or 2nd ml fall in love with mc (this one is the most mind boggling question) it's considered horrible writing. Mc is better off being a side character that has 3 panels every 5 chapters because she's not even remotely interesting, I'd say she's as developed and memorable as a random person part of a street crowd.
I guess it's alright if the target age for this manga is less than 15. The art has its charm.