What is the ruling on repeated heartfelt promises to Allah that are not fulfilled?

A vow is not established by mere intention; rather, it requires an utterance indicating commitment, as stated in the verse: "As for the formulation: It is stipulated that there be an utterance signifying commitment. Thus, it is not established by intention, like other contracts." Allah has forgiven this Ummah for what they contemplate inwardly, as long as they do not act upon it or speak of it. Therefore, nothing is binding upon you merely by these thoughts.