I think my reasons are somewhat valid whether you agree with me or not

1. Sungmin's ideal woman

cr: http://viviankang.tumblr.com/post/5901316763/heart-it-know-what-super-juniors-ideal-girl-look

- Sunny's profile

cr: http://www.popularasians.com/forum/showthread.php/31988-SNSD-%28Girls-Generation%29

2. Sungmin is treating Sunny differently from other SoShi's

- http://www.youtube.com/watch?v=udW4n__2pWY

----- start at 3:00

(I don't know, as soon as he heard SNSD won, he immediately went near Sunny. You can see that he was talking to her saying, "Chukahae" but Sunny was busy talking to Taeyeon. And out of all the SoShi members, he only hugged Sunny/ Note: He was the one who pulled the hug, you just didn't see clearly from this angle)

- http://www.youtube.com/watch?v=fc3zHATe8Yg&feature=related

when it was Sunny's turn, he froze, as if he was really watching her intently

3. I don't know, maybe this one is a little weak

http://www.youtube.com/watch?v=owZ_O5hsL-c

when the MC said that Sunny was a little angry, Sungmin just looked at her, studying if she really was. But then, Sunny smiled at him so maybe he was a little relieved

http://www.youtube.com/watch?v=jkOrtbrodsI&feature=related

this is too sweet!!!! I mean, he wasn't looking at Sunny at all but he knew she was struggling (in a cute way) and as soon as she offered him the drink, he took the bottle so fast!
*They drank from the same bottle*****

4. This video

http://youtube.ng/watch?v=Gd6v3k30D5U

Sungmin claimed that he doesn't have a girlfriend. But said that he has someone special. And since they're not official, he adresses her formally. Sungmin, when you say formal? As in you call them with a -ssi? Like this?

[ http://www.youtube.com/watch?v=JqVkv067F-4&feature=related

Even Ryeowook gave us a hint. He chuckled when he heard Sunny-ssi, I thought Sungmin and Sunny are "friends". Why did he have to be so formal? I'm not saying it's because of the previous vid, but when I watched ChunJi radio, he addresses her as "Sunny-ah". Maybe he doesn't want to be obvious. ]

Another is that, he said they do not eat outdoors. But eats together whenever they can

cr: http://www.allkpop.com/2012/05/sunny-invites-sungmin-as-a-featured-guest-on-invincible-youth-2#disqus_thread

Call me crazy, but I'm definitely buying this!!

Sungmin said they are not official, to which is quite similar to Sunny's answer on Star King

cr: http://www.allkpop.com/2011/09/sunny-reveals-that-less-than-the-majority-of-the-snsd-members-are-currently-in-love

in relation to this, she said that it doesn't have to be a commitment, just pure innocent love

5. Sungmin once said he wants to write a song for the one likes?

Maybe he actually did

http://www.youtube.com/watch?v=z5fsldq2VUU&feature=related

He even said "I love you"

I just wanted to share these

http://www.youtube.com/watch?v=Z_fzD9sPYOU&feature=related

Awww, he misses Sunny :((

http://www.youtube.com/watch?v=l4avaYY3PzE&feature=related

6. Even Jessica knows it

http://www.youtube.com/watch?v=JaYj_TdSOOY&feature=related

@3:20, Jessica pulled Sunny near Sungmin

cr: http://snsdkorean.com/2012/05/18/sergeants-thoughts-on-who-will-get-married-first/

- something's fishy about here. wanna know what? Other than Jessica, Sungmin was also a guest on this episode!!!

7. SuperGeneration know it too

http://www.youtube.com/watch?v=Gmzv1jgqLDg&feature=related

see for yourself

8.Evn other celebrities know it

cr: http://www.allkpop.com/2009/07/super_juniors_sung_min_clarifies_dating_rumors_with_snsds_sunny

that's for now. I'm off attend something important