Psychological ED?

In February I started dating a woman I met through a widow support group. We both lost our spouses last year. I am 40 years old, she's 30. It had been a long distance relationship but she's moving here later this month.

I had trouble getting and keeping an erection and talked to my doctor in April or May, he prescribed Viagra, which has been effective. I don't have trouble getting a good erection while masturbating to porn. We made some recordings of us having sex, and watching those I can get and keep it up really hard. She's beautiful, sexually adventurous and has a good appetite. Best lover I have been with.

I have been stressing out about this. Why can I have a good hard dick until we get naked and start fooling around? I know that I worry about failing a lot on the drive to see her. Watching porn or our videos can get me hard, so I am thinking it's psychological. Sometimes after we've been together at night, the next day I can get hard enough to have sex.

How do I stop stressing about staying hard?

I'm suffering through a similar problem. I'm also interested in any advice people have to offer. You're not alone.