I was helping a friend do a dauntless delver/cradle and all run. Our 4 man party came across a love puppy at depth 27... The love puppy started to heal us and then started to give me its love, but sadly shortly after it turned to someone else and started to love them instead. Out of jealousy I hit the Love Puppy with my curse vial, the only one I had with me, and it continued to heal the player until it died due to the curse.
The Love Puppy does indeed show true love, even giving its own life to heal others.
Sadly, its in the Love Puppy's programming to cheat on one player with others... The only time you know you have a loyal, loving, and compassionate Love Puppy is if it gives you a True Love Locket.