Justin was rolling on the streets of NYC with his fiancee, proudly displaying the ring she bought for him as a sign of love.
The 2 were leaving Hailey's apartment for a weekend trip to Miami.
In case there was any doubt about their relationship ... Justin posted this pic of the 2 of them making out at David Grutman's house and they were later seen at Komodo restaurant.
TMZ broke the story ... Justin and Hailey got engaged a week ago in the Bahamas after re-dating for only a month. What's more, he apparently knew within days he wanted to seal the deal with her because he asked Stephen Baldwin for his daughter's hand in marriage.