How old are you?
Do you have high blood pressure?
HPB indicates your arteries are stiffening, and that affects...your stiffies. Seriously. Try to do cardio exericise 3 times per week, get off caffiene and illegal drugs, and talk to your doctor about it. Viagra and cialis can help. But they are often not covered by insurance, and Viagra costs about $25 per pill in the US.
And yes, high amounts of alcohol can affect this. So can stress, and lack of sleep. So can drugs. I've heard zoloft can cause this.
I have a long time interest in psychology, specializing in relationship dynamics for 30 years.
(Please note, we give the best advice we can based on the information given in a post. For better advice, please include the age of all romantic partners.)