I'd swear you my sword, but I don't actually own a sword
I pushed a boy out a tower window, crippled him for life for Cersei. I strangled my cousin with my own hands just to get back to Cersei. I would have murdered every man, woman and child in Riverrun for Cersei.
When you play the Game of Thrones, you win... Or you die. There is no middle ground
If you were to marry Cersei, she's murder you in your sleep.