Thank god It's Friday is set in the same school with the same music club as Love Sick. The connection is shown in episode one. Also, both are set up as BL. TGIF has more characters and a set up for multiple couples it sees. Similar vibe between the two of them so far as well. The relation is slight however so I'm sure you could get away with watching TGIF without watching Love Sick. However, I would recommend watching Love Sick first because it's really good and having seen it you can more fully appreciate the setting of TGIF.
Bad Buddy reminded my of Love Sick, which I would deem one of the original Thai BL dramas. The main characters of both dramas are in a school setting (College/High School) who seemingly have no relationship to each other according to the people around them. The relationship growth from no relationship to friendship to lovers can be found in the dramas.
It could be the blue shorts, but ITSAY gave me Love Sick vibes from the very beginning. Both have that raw, vulnerable, and uncertain feeling that accompanies young love and discovering one’s self. The filter used in ITSAY also imparted a retro feeling that took me back to the early days of Thai BL.