Sos For A Dear Friend

I've been hearing and reading about it but I never knew that my friend's fiance who she has dated for more than 3 years,has the problem.Am talking about inability to satisfy a woman in bed.He has weak erection and before he would insert well,he has poured.My friend said he one time used viagra which he hid from her,when she knew and confronted him,he had to confess that he used it to please her. Now the problem is that the drug is too costly and they need a lasting solution to this problem as I turely know they love each other and can't part.Please a doctor in the house should please help,are there drugs that can help correct this?