Around 2am the decision-making part of your brain is running on empty, while the emotional part is still fully awake. That's why a message written at that hour comes out sharper and far more final than the one you'd write in daylight.
It's not a willpower problem, it's biology. Sleep deprivation weakens impulse control and makes small things feel like emergencies. What feels true in the moment is often just exhaustion talking.
One simple rule helps: write it, don't send it, leave it as a draft. Reading it back in the morning usually means softening it a lot or not sending it at all. Sometimes filling that gap with a song or a few quiet minutes does the same job.