Is what the questioner is doing correct, by inferring that his ablution is not invalidated because he cannot swear that it is invalidated, in order to avoid obsessive doubts, knowing that he does not actually intend to swear but rather takes it as a rule?

He who is afflicted with waswas (obsessive whispering) concerning purity should not pay attention to it, nor should he abandon the certainty of purity merely due to doubt. The fundamental principle is that what was, remains as it was, and certainty is not removed by doubt. The Prophet, peace and blessings be upon him, explicitly stated this by saying: "No, [he should not leave his prayer] until he hears a sound or perceives a smell." This hadith is a great principle in Islam. Whoever is certain of purity and then doubts its invalidation should build upon certainty, which is purity, and should not pay attention to this doubt.