Erectile Dysfunction? Help?

I am a college student and I’ve been hooking up with this guy for about a year. So the first time we had sex, he couldn’t get it up completely. He felt hard but as soon as he was about to enter my *palace*, he would lose it. I know he’s into me because we have slept together many times. He can always get it up but it’s never completely hard. Is there anything I’m doing wrong, or is there anything I can do to make this better? Tonight he came over and I went down on him for a bit but he still couldn’t get completely hard (which usually he does when I give him oral).... PLEASE HELP!