As has already been mentioned, the buyer may have lost interest. If that is indeed the case then the buyer may well have decided to purchase the item from another seller, in which case your counteroffer has ended up losing you a sale.
In the event that the listing ends with no buyers then relist the item again at the counteroffer price if that's what you'd be willing to accept for it. If somebody else who didn't see the listing the first time sees the relisted version of the advert and decides that the asking price is acceptable then you may be able to secure a sale the second time, albeit to a different buyer. It's also possible that the person you sent the counteroffer to may end up spotting the relisted advert and change his/her mind about deciding not to buy at that price, especially if he/she hasn't been able to find a similar item elsewhere in the meantime.
