What is the ruling on saying: "Allah is dearer to me than such and such," or "I will not allow the pleasure of food and overindulgence in it to stand between me and Paradise," and then contradicting one's statement? Does this count as an oath or as disbelief (kufr)?

The phrases mentioned are neither disbelief (kufr) nor do they constitute an oath necessitating expiation. If the intention behind them is to prevent oneself from indulging in permissible pleasures out of fear of falling into the forbidden, then this is a commendable form of piety (wara'). However, if the intention is to forbid what is permissible, then nothing is entailed by it, and no expiation is required according to the majority of scholars. A Muslim should emulate the Prophet, peace and blessings be upon him, in his eating and drinking.