The healthy kind of relationship is two complete humans sharing a table, not two halves fighting over one chair.

Two people who each have a life bring something to the table. Two people using each other to feel complete end up competing over the same small supply, which is why that version feels so intense early and runs out later. Need is not the same as closeness, though at the start they are hard to tell apart.

Check what you still do on your own: friends, work you care about, something that is yours. Keep those alive during the good stretch rather than only after trouble. The measure is whether you would still have a life if the relationship paused, and whether you would still want it.