Rebound

So I was talking to this guy after me and my ex broke up... I told him I was vulnerable and I just needed a distraction he was okay with that we never dated just talked now me and my ex are getting back together and we decided that all is forgiven but we have to block anyone we spoke to Inbetween our break...

How do I tell this guy who really likes me and was a rebound to me that I can’t talk to him.

I’m not the type to ghost someone but I don’t want him sending bad energy my way.