undeviating, unswerving(adj)

going directly ahead from one point to another without veering or turning aside

"some people see evolution as an undeviating upward march from simple organisms to the very complex"; "a straight and narrow tree-lined road unswerving across the lowlands"

steadfast, staunch, unswerving(adj)

firm and dependable especially in loyalty

"a steadfast ally"; "a staunch defender of free speech"; "unswerving devotion"; "unswerving allegiance"

unswerving(Adjective)

Not deviating; not yielding or straying or varying.