I keep losing my erection during sex and it’s making me miserable

DEAR DEIDRE: LATELY, I keep losing my erection during sex and it’s making me – and my partner – miserable. 

I’m wondering if using Cialis will help me stay hard. 

I’m 42 and my partner is 39. We’ve been together for five years. 

Everything worked perfectly until last year, when I started going soft midway through our lovemaking. 

The first time it happened, I put it down to having had too much to drink.

Then it began to happen every time, even when I was sober.