Not sure what has happened, but just to be sure. All members are looking for a good match (for them) and communication before an agreement is made is just that. Before a sit is confirmed both parties can pull out for any reason. I would think the polite way would be to say clearly that one is moving forward, but even members who don’t - hosts or sitters - can pull out. Nothing is final before a host has sent an invitation to sit AND the sitter has accepted.
I understand that this can be stressful, in particular for a new member learning to navigate. All members should have a plan B if (even) a confirmed sit falls through. If you want to, you can get help with your listing, maybe a few tweaks to get the right applicants. If so, you can add your link to your forum profile:
How to add a listing or profile link to your Forum profile!
Best of luck!