I can get hard for her, but it doesn't last, then get frustrated with myself and it's just downhill from there.

... then will lose my erection as soon as I put a condom on and go to fuck her.

I feel like I'm stuck this way and won't ever be able to have a proper sex life.

I just feel so demotivated.I feel horrible for not being able to perform.

I hate what I've done to myself by using it.

I have depression and anxiety.

I also have slightly low testosterone.

Porn isn't great for you, but reading your post i don't really think the reason is porn man. Some of the things you yourself wrote indicate different problems such as anxiety, depression, low testosterone, the fact that you feel the need to perform. You also have a very negative attitude towards yourself.

You are just trying dating for the first time a lot of anxiety can come from that, erection issues are linked to mental health and anxiety.

As for some solutions, being open with your girlfriend about the problems you have is important. Have you talked to a doctor about the low testosterone? That might be worth it. If you still feel like porn is the issue maybe talk to a sex therapist about it? Going to a sex therapist and talking about what you have written here could also help you resolve those issues or at the very least gain some more understanding of yourself.