She could certainly be allowed to be cheesy. He would be plenty more in the future simply because that cheese was about the closest thing to the truth they could get to convey how strong their feelings were. Still if he wasn't busy indulging in the delights of Lucy's body he would be preening himself quite a bit after hearing her words.

"My mate. In soul and body~" Natsu answered back with a murmur filled with nothing but adoration and desire before he claimed her lips in a deeper kiss this time.