Need help understanding

My boyfriend and I have been together for over a month now (long distance) and just spent an amazing weekend together. Everything about being with him was just so perfect and having to let him go back home was one of the hardest things I've ever had to do. Being together (non sexually) is so easy with him and he makes me feel like I'm the most amazing women in the world. Now when it comes to being sexual and trying to have sex we are both very into it and turn each other on but when it came to actually having sex my boyfriend begins to over think about the act and worry wether or not he's doing everything right and then even though he's turned on and wants to have sex his (member) seems to have other plans. He says he has performance anxiety but I feel like it's me and that I'm not good enough or sexy enough for him to be able to stay hard for us to connect in that way. He reassures me that I'm not the problem but I need help understanding what the issue seems to be and why even though he wants me that way that he's not able to "keep it up".