Actor Gregg Sulkin is divin' head first into his summer romance with social media influencer and model Freya Tidy -- the cuffed up couple sparked social media with their summer-toned bods on display ...

Flashin' their backsides, Tidy (22) donned a stringy bikini which totally complimented her model physque ... Meanwhile, Mr. Sulkin (33) draped his shredded back in nothin' but a white bath towel.

The hunky star -- who gained fame playing JJ on Disney's "As the Bell Rings" -- rocked an off-white button down and captured Hawaii's beauty and serenity with this scenic snap ... Views for days!

But more importantly, he got back to the shirtless vacay regime, and there's more where that came from 😜!