Nether Portals Don't Work Separately

Portals made in the overworld only ever connect to the first portal made in the nether, while portals made in the nether only ever connect to the first portal made in the overworld. When I go back through the portal in the nether after creating a new portal in the overworld, it chooses randomly between the two portals in the overworld and sends me to one of the two. This has become a problem for nether travel and exploration for me and has also caused a lot of wasted time as well. Considering this information, nether highways are also impossible to make.