Certainly seems that way ... 'cause the ex-NFL superstar brought his Miss Universe girlfriend to the Tebow Family Thanksgiving -- a sure sign that things are getting THAT serious.

Tim and Demi-Leigh Nel-Peters -- Miss Universe 2017 -- have been dating for a while now ... and they've been getting super cozy with each other the last few months.

Remember ... the South African model wished him a very public "happy birthday" back in August AND the two had a date day in New York with DLNP's fam in September.

In fact ... Demi even hinted she was "falling in love" with the minor league baseball star after the two hit up a Florida game last month.

But, the couple took things to another level last week ... when Tim brought her to the fam's turkey dinner.

"My first American style Thanksgiving with the sweetest family," DNLP said of the holiday ... "Grateful for an incredible year and everyone I got to share it with."

Tim never got a ring in his 3 years in the NFL ... but we wouldn't be shocked if he bought one pretty soon!!!