I know DHX and Hasbro can't come out and say it, cause of 'decency' or whatever that is. But with the frequency these past few nudges have been coming out, it's gives the impression that if they could come out and say it, they would. Yes, the term 'joined at the hip' is often used to describe two people who are almost always together. But it more correctly indicates an intimate relationship, or sexual innuendo. 'Joined at the hip' literally means two people who are always having sex.
@Lawful Girly You know, the main characters actively hug all the time too. Friends can hug each other openly.
This kind of interaction doesn't really say anything beyond them being close, and that can mean as friends OR lovers. Chalk it up to headcanon, or otherwise how you personally want to interpret it, like it's pretty much always been, as there is no canon answer.