You want a bridge. Like Jabagram or Emulsion. But there’s a limited set of features that will work. For example, reactions or group admin on telegram can’t be easily replicated over xmpp. And, in any case, we are talking more about having messages and media on both rooms, on either side, replicated. That way, users on telegram (e.g. your friend) can talk to users on xmpp (e.g. you). Reliability for bridges is not good, there are glitches and messages that doesn’t make it to the other side, whichever that is. I’d say you prefer to self-host xmpp with cherry-picked extensions, like snikket.org