The correct answer is - it lost ocean access.
The relative location, simple means, the relationship of a certain place with other places. It can be anything from physical geographic features, natural resources, economy, ocean/sea access etc. that are determining the relative location of a country. For Ethiopia, the very important aspect of its relative location is the ocean access. When it lost access to the ocean waters, and is surrounded with the likes of Djibouti, Somalia, and Eritrea that do have access to the ocean, it changed the relative location of the country because it became economically dependent from its neighbors. It became a landlocked country, so any dispute with the countries that have access to the ocean can be a huge blow for the economy of the country, thus putting Ethiopia in a very bad situation where it is heavily dependent and blackmailed by its neighboring countries.