. . . three heads has the dragon . . .
. . . three fires must you light . . . one for life and one for death and one to love . . .
. . . three mounts must you ride . . . one to bed and one to dread and one to love . . .
. . . three treasons will you know . . . once for blood and once for gold and once for love . . .
three fires: (the pyre where she burned Drogo, Killing the undying warlocks, maybe Jon Snow?)
Three Mounts: (Drogo, Her second husband in Myreen, Jon)
Three treasons: (Her brother, Black dude with the vault, Missandi? or the dothraki girl he was in bed with?)
My theory is...
3 fires you must light...
One for Life = The fire Dany used to bring her dragons to life.
One for Death = The fire Dany used to kill all the Dothraki Khals at the same time.
One for Love = This fire will most likely be for Jon Snow.
Dany will probably 'light the fire' inside of Jon that he lost when Ygritte died.
Since then, he has been 'very distant' with almost every woman in his orbit.
Or Dany could 'light the fire' inside Jon that he truly needs... to defeat the Army of the Dead.
The monster swing he takes at the end of this clip is truly DEVASTATING.

Looks like someone 'lit a fire under his ass'... to split some wigs.
3 mounts you must ride...
One to Bed = This was Daario Neharis. (Their relationship was based on Lust. That's all.)
One to Dread = This is her 'dreadful' dragon... named Drogon.
One to Love = This was Khal Drogo. (or soon it could be Jon Snow

)
3 treasons you will know...
Once for Blood = This might be Tyrion (or Varys

) who might soon undermine Dany... to save Jamie.
Once for Gold = This was Xaro Xhaon Doxas, who died in the vault of Qath. He stole her dragons for Greed, Power & Gold.
Once for Love = This was Jorah Mormont, because he said: 'I have loved you'... right before she exiled him the 1st time.