I was planning to sell my house and I have signed the commitment, but now I want to give up. What can happen if I don't sell my house? What should I pay?

That depends on the terms of the commitment you signed and how far along the process has gone. The buyer coiuld sue you for their costs incurred.

It is also possible for the buyer to sue for the sale to go through... I've seen it happen more than once.

So depending on how bad you DON'T want to sell, and / or how bad you think they want it... I'd be prepared to make it worth their while to forego the sale.