Gypsy Rose Blanchard is remembering her best times with her late baby daddy, Ken Urker ... posting several heartfelt photos and videos from their relationship ... and calling it her "greatest love story."

The social media star took to Instagram to bid a fond farewell to her former fiancé ... sharing videos of him planting smooches on her, singing his heart out, and playing with their daughter, Aurora.

One memory looks straight out of a Disney movie ... a video where they share a piece of spaghetti just like in "Lady and the Tramp."

GRB captioned the post, "You will always be my greatest love story. You will be remembered and loved forever. ❤️."

We broke the story ... Ken was found unresponsive in Louisiana on Thursday and pronounced dead. Gypsy's brother Dylan found the body, family sources told us.

Gypsy told us it's believed Ken died of an overdose ... because he was found near an unidentified substance. It's surprising because Gypsy said she doesn't believe Ken ever had a drug problem.

Ken's sister Autumn is calling BS on Gypsy's narrative ... alleging she's telling lies about him -- just like she allegedly told lies about her mom, Dee Dee.

Foul play has not yet been ruled out by investigators looking into Ken's death.