There is literally no flaw in this drama, the actors were great, the storyline was great, the production was also great.
Trust doesn't come right away with love and this drama did a good job in showing that with Third. They also showed one-sided love and being in love with your bestfriend. What I also love is the way they write the characters, I relate with Third so much and I also loved Khai's character development.
Being a big fan of Thai BLs, most of them doesn't have a great storyline but Theory of Love is just different, the plot is just so great that I cannot compliment it in words. I recommend this drama but please take note that it's a story where you cry a lot.