Julianne Hough -- New Boyfriend Delivers After Walk of Shame

It's getting serious ... Julianne Hough's face-sucking new bf performed the walk of shame from her place this weekend -- but followed up like a champ by sending her flowers.

Ryan Seacrest's replacement is Ari Sandel -- an Oscar-winning director. We posted pics of the couple getting hot and heavy in a restaurant ... and it appears they've upgraded to sleepovers.

Shortly after Ari reportedly left Julianne's West Hollywood pad early Saturday morning -- which also happened to be her 25th birthday -- he was seen walking into a flower shop ... but leaving empty-handed.

Walk of shame sources tell us a short time later ... JH got a knock at her door and a fresh bouquet of red roses.