The heartbroken girlfriend of London Bridge terror victim Jack Merritt vowed in an emotional tribute to “make a difference” in his memory.

Leanne O’Brien remembered her beau, a 25-year-old Cambridge University graduate, on Monday in a Facebook post, just three days after he was killed in a stabbing rampage in London.

“My love, you are phenomenal and have opened so many doors for those that society turned their backs on,” O’Brien wrote. “Together, we will make a difference.”

Merritt was working as a coordinator at a Friday conference on prisoner rehabilitation when he was attacked by 28-year-old Usman Khan, a convicted terrorist who was released from prison last year, police said.

Merritt was fatally stabbed along with fellow Cambridge grad Saskia Jones, 23, authorities said.

Three other people were also injured in the rampage before Khan was wrestled to the ground by onlookers, police said. He ultimately was shot dead by police on London Bridge.

Merritt’s girlfriend led a vigil Monday for those killed in the terror attack.