Mackenzie Shirilla's late boyfriend Dominic Russo sent her a chilling text message in the weeks before she killed him in a car crash ... talking to her about life being short.

In the text message, obtained by TMZ, Dom tells Mackenzie ... "Kenzie u know i love u but i dont think we should be together at this point there isnt very much time on earth."

Dominic proceeds to mention constant fights and breakups that don't stick ... telling her they need some time apart.

He adds ... "i dont want u to think im abandoning u i wish it could work but i dont think its going to at this point especially with the threats we should just breakup so we can both fimd happiness somewhere else."

Dom sent the text on July 2, 2022 ... about four weeks before the fatal crash that killed him and his friend, Davion Flanagan. Mackenzie was driving 100 MPH when she crashed into a brick wall in Ohio, and she was later convicted of murdering them. Prosecutors said the crash was intentional.

For her part, Mackenzie's maintained it was all a tragic accident and she experienced a medical emergency behind the wheel. She's behind bars and is eligible for parole in 2037.