@C Money  
She puts her hoof on his MOUTH because she is already aware he has a crush on her. She constantly uses his affection against him for her benefit. (Being her pin-cushion, taking out her garbage then insulting him for smelling, the ruby heart incident, etc.)
 
She also pines on other stallions and COMPLAINS to Spike about it while being well-aware of his crush on her.
 
Not to mention they share little in common. Yes, they both like gems, but for different reasons. Can you think of ANYTHING they share despite that? And don’t give me the bullshit of “opposites attract,” because you need to have common ground in order to be attracted to someone. A balance of differences and similarities so you can trust the individual but also be interested in them.
 
And isn’t the only thing Spike sees in her is her beauty? He admires her determination, I suppose. When he is asked why he does what he does, he simply says she is “incredible” without any other explanation. Incredibly beautiful, maybe, but the admiration of beauty is not a concrete base for a long-lasting relationship. But he is a child and doesn’t know any better, about relationships or otherwise.
 
She calls him a friend. The boy bound to have his heart broken.
 
Also, I’d say Spike is ten while Twilight is seventeen. Enrolling into Celestia’s school at age seven is pretty reasonable considering we do the same. It also matches EqG’s teenage representation of Twilight. (Also, if you bring up the CMC’s ages, remember there are differences AND similarities, their universe and Equestria’s aren’t mirrored.)

@TexasUberAlles  
Well ain’t that a shitload and a half of speculation.

@VermiIIion  
That’s the vibe I get from rarity. She seemed to reveal her feelings more deeply when Greed Spike became normal Spike, and they both seemingly plummeted to their deaths. I got the vibe when Rarity put her hoof on Spikes lips. For all we know, it could happen. But at the same time, it could also not happen. All we have to do is wait and see.

@Fwelin  
ffs don’t try to argue with a duckbadger in shipping goggles what are you thinking

@Fwelin  
Addendum: So, if Twilight is 20ish, then Spike is just entering his teen years. That’s a pretty big gap right now, even if it won’t be in 10 years.

@C Money  
Twilight’s age is extremely ambiguous, but she was larger than the 5 year old Sweetie Belle and her friends in For Whom the Sweetie Belle Tolls. Twilight was likely around the age of 7 when Spike was hatched.
 
In addition, I really doubt her parents would let her walk around Canterlot alone if she was only three years old.

@C Money  
Still unlikely to happen because Rarity sees him as a younger brother and they share nothing in common.

@Align  
Spike was hatched from Twilight was age 3 or 4. So whatever age Twilight is, Spike is only three or four years behind. He’s almost as old as Twilight, but is young in Dragon years. Because he’s lived around ponies he should actually be pretty mature for someone his age.

@Align  
think dog years

@C Money  
wat

Sorry, but spike is actually around Rarity’s age. He’s just genetically young because he is a dragon, when he’s about 19 or 20 years old in reality.

@Katamariguy  
Because unknown reasons.

Why the hell is sweetiemash a thing?

sweetie belle is the most dangerous pony in equestria?!!
 
or at least the best fish murderer out there.

Spikebelle still sails!

Brilliant.