Struggle to get an erection, and then maintain it.

Okay so I'm a 20 y/o virgin and I recently got a new girlfriend. The last four times we've tried to have sex I've gotten ED, however the last 2 of those times I was eventually able to obtain an erection while she was giving me a handjob (and this was only because I pictured some of the porn I watch in my head), anyway the handjob finished with me ejaculating therefore making it even harder to get an erection to actually have intercourse with her afterwards. She doesn't know I'm a virgin and I'd like to keep it that way. What can I do about this anyway?