Question about OLTL... Eli & Seans brother

I have not watched any soaps for about two months and I am wondering what Eli has on Seans brother Greg (I think it is his name, he isn't on often enough for me to remember it) that has Greg doing whatever he is doing or did to Tea? I really liked Eli (and with Blair) until he all of a sudden turned into this killer of 5 people. Did they do this because Tea is dead and they want to put Todd and Blair back together?

What these characters can't move on with anyone else? (GH does it also which I hate because sometimes they have just run their course example Sam and Borg Jason, Lulu and Sunnydelight Dante, Patrick and Robin to name a few.)