Adding e.preventDefault() in the onClick handler will prevent the form submission.
<script>
$(document).ready(function() {
$(document).on("click", ".alert", function(e) {
e.preventDefault();
bootbox.confirm("Are you happy with the decision you have made?", "I have changed my mind", "I am happy with my choice", function(result) {
if (result) {
console.log("user confirmed");
} else {
console.log("user declined");
}
});
});
});
</script>