Looks like the romance between Paris Hilton and her very sexy supermodel beau River Viiperi is heating up!

The two have been friends over the past year and hung out every day and night during New York Fashion Week. Whether spending time together at runway shows, parties, restaurants ... or riding rollercoasters at Six Flags Magic Mountain, these two are inseparable.

A source at the amusement park tells X17online, "They looked so beautiful together, like a real life Barbie and Ken. Everyone was stopping Paris for pictures and she was so sweet with everyone. She and River walked thru the park hand in hand. They looked so happy together."

We love these lovebirds together - what a HOT couple!