as someone who has a super busy best friend, it can be hard. especially because you start to feel that they just don't like or care about you enough to make time for you, even when it's not the case. so I can see where he is coming from, but obviously, if you are just busy and you really don't have the time, then it's not your fault and it's not great that he's making you feel bad about something that is out of your control. I'd say to just try to make sure he knows that you do actually care about him and value him as a friend, and just try to help him understand that it's not just you not wanting to meet, but the fact that you can't. and maybe try to find some time to meet, even if it's not super soon and not for long.