Thanks for your query.Based on the fact that you have erectile dysfunction
and taking Viagra.You are losing erection sometimes before sexual act,This is not abnormal and does happen once in a while.This is mostly mind related and due to anxiety
.Try to convince your girl friend and consult some qualified sexologist
for guidance and advice to delay ejaculation and losing erection .You may take Tab Dapoxetine
along with Viagra to sustain erection for a long time.