I was with a girl tonight that I've seen once before. We didn't have sex the first time.

When we were lying together in her bed, kissing and groping each other, I was hard.

Afterwards, when I was eating her out, I was hard.

I tell her to come give me a blowjob. As she moves towards it, I slowly start going soft until I'm completely flaccid. I try jerking off. Doesn't work. She tries jerking me off. Doesn't work. No blowjob. No sex. Can't get hard.

Even when I get hard, it usually seems to be a struggle. Like I don't stay hard very long. And I have to make a conscious effort to keep myself hard. I don't feel rock solid, I feel like I could always go soft at any moment.

What do I do about this? This is completely destroying my confidence. How am I supposed to be alpha, be a man, when I can't perform sexually?

EDIT: Until recently, I've never had this issue. It's all been within the past year or so. I'm 22.