The belief that manufactures despair
Answer it in your head first.
You made tawbah in Ramadan and meant every word of it. In August it happened again. Does that mean the tawbah in Ramadan was insincere and did not count?
No, and the report in Bukhari is explicit about it. There a servant sins, asks forgiveness and is forgiven, then does it again, and again, and is forgiven each time. The resolve is a resolve made at the time of repenting. Later failure does not reach back and cancel it. The belief that it does is not from the sound material, and it is the belief that manufactures despair, which is the state the Qur'an actually warns about.