Elijah said he's only been truly in love twice in his 1,000 years of living. Celeste being #2. But Celeste isn't who Elijah thought she was or romanticized. As Sabine she transferred all the power from the sacrifice of the four girls to herself to resurrect 3 other witches from different eras (all who have a bone to pick with Klaus and Marcel), which was the reason (as far as I could tell) why the girls remained dead.
Elijah and Hayley have hit a rough patch but I hold out hope for them but Celeste's return doesn't bode well. Remember how Elijah can easily let his heart over look someone's evil flaws; there was Katherine whom he still held out hope for. But who's to say Elijah will give his heart to Celeste again.