kaddict_since2016:

The  other dramas I have watched that are similar are  My heart is twinkeling ,Delightful girl Choon Yang ,Love & Secret ,The Greatest Marriage  and Cruel Romance they have a similar kind of leads or second leads do you know any others?

Chun Woon Tak was especially good I kept wishing that they axed the third sisters' (She annoyed me!!)role to give him more screen time

I didn't watch those dramas before. I think the last 2 obsessive guys I've seen were in Manhole (the psycho/stalker guy had more screentime in the later half) and Roy Leh Sanae Rai (2015) the ML tricked the FL into falling in love/marrying him to take her inheritance money but he's still obsessed with her even when she finds out the truth/hates him. Also Let Me Introduce Her was a bit similar to Love in Sadness at first but I think Ryu Soo Young's character is more psycho than Jo Hyun Jae's.

Then you should try them I would definitely recommend them.