Gaster x Toriel - Gastoriel.
Toriel x Gaster - Toaster.
This ship is them truly loving each other!
Before Toriel is ever with Asgore! and after leaving him as well! Toriel moving on being back with her past love. But only if Gaster returns from the Void. Until that happens he visits Toriel in her dreams at least until he returns. Your choice. Oh and to make things more interesting about this ship. Only Toriel remembers Gaster. She doesn't know why though. Confused as to why nobody else remembers Gaster, as far as she is aware of. - P.S She never cheated on Asgore.