还 is someone or something still in the middle of a condition and not end yet. So when you use 还 normally you don't use 了 in the same sentence.
I am still sick.（not recovery） 我还在生着病。（没有康复）
I am still in love with her. 我还爱着她。
还+verb+着 is a little bit like present progressive
了 normally is used in a sentence in past tense.