Indeed, the pair kept any PDA to a minimum at the Los Angeles hotspot's "Red, White and Bootsy" bash, but the source says Jenner and Clarkson's "relationship has been getting stronger over the last couple of months."
"They're very openly affectionate when they're comfortable ... with friends or alone on a date," says the source. "They enjoy low-key dates like quiet dinners where they won't be bothered."
And though another insider recently told WHO their relationship wasn't completely "serious" yet, the source adds the duo – who have been linked since March and also attended Coachella together – are definitely heating up.
"They really like each other and Jordan is super into Kendall," says the source.