"I'm doing this because I love you" PLL theory
Ian said "I'm doing this because I love your sister" to Spencer right before he TRIED TO KILL HER... And there is no doubt in my mind that that's what Ian was trying to do; that was his motive and he said it out loud.. I'm emphasizing this because it's weird.
Melissa argued with Spencer a LOT, yes... But why would Melissa's husband need to prove his love to her by KILLING her sister? Is it because of Spencer and Ian's kiss? Perhaps Melissa has MAJOR jealousy issues to the point that Ian felt the need to kill any girl with whom he cheated on Melissa. Maybe he already knew about Melissa's issues and was scared of what Melissa might do if he didn't kill Spencer.
And perhaps the reason he knew this is because that's the way he had to prove his love for Melissa in the past... when he cheated on her with Alison. Maybe he tried to do away with Ali "because he loves [Melissa] too. After all, Melissa DID warn Ian that if he ever saw Alison again, "someone would get hurt." And she sounded like she meant it. This is interesting because Ian DID see Alison again, and he said something similar to Ali regarding revealing the infamous PLL videos. This would make a lot of sense. What if Melissa never got over that jealousy and she is the one who killed Ian, too?
When Melissa has been asked out loud what she thinks happened to Ali, she's latched on to whichever theory the media believed that week. I think Melissa thought she killed Alison that night, then found out somehow that people thought Ali was alive and she joined and/or formed her own "A" team so she could find out for sure? She could be the one in charge or the person who "stole the game" from Mona. She was the one, according to Wren, who "called CeCe to tell her Mona was in Radley because she knew "CeCe and Mona had a mutual enemy." Remember when CeCe hated Alison and her "she devil" friends for getting her kicked out of school? What happened to that? Suddenly she and Ali are exchanging illegal passports and killing people for each other? Wren is the one who initially told the story about Ali getting CeCe kicked out of school, and obviously he found that out from Melissa. ONE other person (CeCe's roommate) confirmed that CeCe felt this way about Ali and the girls.
I would hope the writers have reasoning for some of the things I've mentioned above. Maybe Melissa had a plan to kill Alison, and she sent people to get REALLY close to Ali, close enough to gain her trust. Before the Shana reveal, Ali believed that some people were helping her. Those people were: Mona (at the very beginning when she thought Mona saved her life, before she knew MONA WAS A..., Shana (and look at how that turned out for Ali), Noel and CeCe... Maybe Noel and CeCe aren't really on Ali's side either. Maybe they were all working for Melissa. Maybe this is her "game."