Romance J-dramas? Sometimes, it seems to me like an oxymoron. But here are the ones I would suggest :
2018 : Ossan's Love (it's a BL)
2017 :
- Boku, Unmei no Hito desu (not the best romance drama ever, but it's still entertaining)
- Kahogo no kahoko (pretty good)
- Tokyo Tarareba Musume
- Totsuzen desu ga, ashita kekkon shimasu (I didn't like it, but romance is not my favorite genre).
There is also the currently airing Bungaku Shojo and Kemono ni Narenai Watashitachi but I've not completed the first one and not started the second so I don't know how good they might be.