Erectile Dysfunction. Sexualy aroused.

Sir i am unmarried,more than last one year i facing erectile dysfunction problem,i saw a YouTube video there suggest erectile dysfunction need early treatment and i started my treatment with tadalafil 2.5mg tablet ones in twice a day at same time st -3rd tablet gave me a better erection whene i am aroused but when take time 4th tablet one day break after 3rd tablet that my erection was proper but treatment issue I don't miss the 4th tablet, after take 4th tablet my sexualy arousal is gone after one day break i take my 5th tablet of tadalafil 2.5mg but my erection was totally gone,i am very depressed what happened in after take 4th & 5th tablet, please suggest what can i do,st-3rd tablet I don't have long lasting erection, erection only happen when i am sexualy aroused.