Watari is in love with Tsubaki. Anything else is facade and/or shallow infatuation.
Proof? Talk between him and Kousei in music classroom in Ep.2 "it's only natural for the girl you're crushing to be in love with someone else". And again talking with Kousei in Ep.11 "I'm me, you're you. I can't appeal to Tsubaki's maternal insticts".
"Your Lie in April" doesn't refer to Kousei, but to Kaori
.Proof? When Kaori meets Kousei, even though she's there for Watari, she seems to know everything about Kousei: his background, his achievements, the fact that he plays piano. Of course, she plays it off as him having "celebrity" status in the world of classical music.
As mentioned on the main page, Kaori has a fatal disease and in chapter 37, elects to a risky surgery that she knows will only prolong the inevitable but she does because she made a promise to perform together with a boy she met in April and in chapter 43, there's a letter she writes mentioning "a lie in April".
The "Lie in April" bit is that Kaori wanted to meet Kousei the whole time, and not Watari at all.
- Confirmed in chapter 44. The "lie" is that Kaori is not really in love with Watari at all. She used that lie as a roundabout way for her to be introduced to Kousei.
Despite what Kaori thinks, Watari does love her.
Throughout the series, he doesn't hook up with any other girls, and his last scene is looking at Kaori's picture on his phone
. He just wants her to be happy
, and he knows that she'd be happiest with Kousei.
Saki Arima abused Kousei, not because she wanted him to get better at his piano skills, but because she was a sadistic bitch and a sociopath.
Think about it, there were so many other alternatives to helping Kousei become a better pianist that there was no other reason for Saki to abuse her son other than that she was a sadistic opportunist. She could have found someone else to help him play the piano, heck, she could have even helped him find another career instead of piano playing. And that scene where she's sobbing and acting worried that Kousei won't survive when he's older was so pathetic that it almost gave me the impression that she was just acting that way to make her look less bad. Most sociopaths have a habit of never admitting they're at fault as well trying to justify their heinous actions so no one thinks ill of them, and her behavior just seems a little too similar to that of a sociopath. If she really did care about Kousei, she would have found other better alternatives instead of putting him through all that traumatic abuse and she's a fully grown adult, she was clearly smart enough to know she didn't have to abuse Kousei just to make him a better pianist and that there were so many other ways of helping him. And no, having a life-threatening illness does NOT excuse her actions.
Alternatively, Saki abused Kousei so he wouldn't miss her.
Saki wanted Kousei to be able to thrive without her and, combined with depression over her lingering days
, decided the best way to act upon that was to distance them and make Kousei glad she was gone
. In addition to training him rigorously for a profession, she made herself a monster to him, ensuring he hated her guts and would surely move on quickly after she died. It definitely backfired and was extreme as hell, but let's face it, well meaning or not, Saki's state of mind was hardly stable by that point in time.
Kaori's incantation in episode 4 really did get heard and answered by something.
Unfortunately, as a spell to summon demons, it came with undesirable consequences. She did get her 15 minutes of fame, but her illness, which had been mostly manageable for the past 14 years, quickly deteriorates and she doesn't live to see the next spring.