How can a young man's desire to marry the girl he loves be reconciled with his father's refusal, given his deteriorating religious and psychological state, and does he fall under the scope of the hadith "There are three whom Allah is bound to help"?

You must fear Allah. You have committed a terrible sin by abandoning prayer, so you must observe it and return to giving charity and being kind to your father and keeping him company in a good way. Do not let despair overcome you. Seek out righteous people to advise your father, and increase your supplications and seeking forgiveness. Remember that among the three whom Allah has حق (a duty) to help is: "the one who marries seeking chastity."