Britney Spears Quality Time with New BF Sam Asghari

Britney Spears has herself a guy who's not just really easy on the eyes ... he's a gentleman too.

Britney and Sam Asghari did dinner together at Gyu-Kaku Japanese BBQ in L.A. on Saturday, and her laugh and smile say it all -- she's having a good time with this one.

Brit's "Slumber Party" music vid co-star posted a pic of the couple doing sushi last month, but when he quickly deleted the post ... we wondered if it was anything serious.

Our Spears sources confirm what these photos show -- it is. Serious, that is.

Not a ton of guys out there who look like Sam, and also open car doors for a lady. #GetitBrit