Belle asked outright at the well if he was trying to get her back (the same question she had in the Crocodile, in fact), and he denied it.
He said, “It’s a bit more complicated.” I think Rumple fully intends for Belle to be his happy ending.
By being the one to give Belle her heart back, rather than letting Will, it’s almost like he’s ripping off a freshly formed scab on a wound that was just starting to heal.
Also, Rumple was extremely forthright at the well, which is all Belle truly wanted, but he knew Regina told Belle to forget. He didn’t offer any of that information to her in the scene in the Pawn shop, which could have changed her view of him.