Is my landlord being reasonable or unfair?

I rent a room from someone. I gave this person about a month’s notice that I would be leaving, but made it clear I’d like to return if the room is still available. I removed all personal belongings and found someone to rent the room while I was gone. Months went by. Now I find out the person that was going to take my place either didn’t show up or wasn’t welcome and I am being asked to pay back rent for the time I was gone. I was never alerted to the fact that my replacement did not work out, and therefore never had the opportunity to deal with the situation at the time. I might have been able to find someone else to fill the space, or even would have considered moving back in earlier.

I think that finding a replacement renter is going above and beyond normal tenant duties. Maybe the landlord thought I wanted the room to be held for me, in which case I would have expected to hear about the replacement not showing up (it’s possible the landlord just didn’t like the person and chased’m off) and be given the opportunity to either move back in, pay to hold the room, or give it up. And if there were any doubt, I would expect the landlord to rent the space out if needed rather than assume I’d be back and willing to pay rent for the time I wasn’t occupying the space.

What do you think about this?