Sorry for the confusion! If you've got the two heart bar filled that means you're at max for a normal relationship. The only way to progress further than that is to ask Everett to be your official boyfriend. Just call him up on Saturday and there will be a new button in the bottom right corner on the date select screen. Hit that to get the option of him being your boyfriend. Or don't get him as your boyfriend and spend time with other people, whatever you prefer :].
I'm so glad you like the game!