I haven't played post 2.1 so apologies if anything has changed but the Duty Finder leaves people with no reason to actually create relationships with players - most of them are on other servers, so you're never gonna see them again anyway. It's a terrible system, relationship wise.

After two months, I have just two friends, despite running dungeons almost every day.

Maybe try running with the Party Finder? I think that matches you with people on your own server. They might be more inclined to hang around.