Is suicide permissible out of fear of committing fornication, especially with the repeated occurrence of sinning with one's fiancé every time?

You must offer sincere repentance for zina (fornication/adultery), with remorse and a firm resolve never to return to it, for Allah forgives all sins. To protect yourself, seek Allah's help and frequently recite the supplication: "O Allah, I ask You for guidance, piety, chastity, and self-sufficiency," and "Keep us away from indecencies, both apparent and hidden." Beware of being alone with a non-mahram (definition) man or speaking with him unnecessarily. Stipulate to any suitor that the marriage contract be immediate so that you become his wife. Suicide is a grave crime; whoever kills himself with a piece of iron, or drinks poison, or throws himself from a mountain, will be tormented by it in the fire of Hell, abiding therein eternally.