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Basically you have to use obvious body language. If you have only 90 seconds, I wouldn't try for much drama, and friendship might be more difficult than something stronger, like love or dislike or irritation.

But there are many gestures and actions that indicate intimate relationships, without speech. Handshakes, hugs, kisses on cheeks, heads, lips, holding hands, walking close together, gentle touches in passing. Eye gazing, for lovers. Leaning in.

Ever notice how, in a restaurant, once in a while you see two adults sit on the same side of a booth instead of opposite sides, facing each other? Those are, almost undoubtedly, newly intimate partners in love. The arrangement is more awkward, both for talking and eating, but touch is *paramount* at the start of a new intimate romantic relationship. They are sitting that way to maximize bodily contact and minimize the difficulty of touching and kissing and having hands on each other, even if the touching is not explicitly sexual. It is touch reassurance.

Of course, a parent and child may do the same, not for romantic interest but still for quick access and touch reassurance. 

Of course, body language can reflect repulsion as well. People that dislike each other don't want to be there. Or it can reflect defensiveness; people fold their arms, pull back, lower their heads, in general if they are not open, they are prepared for attack and instinctively move to protect themselves, even if they are in zero danger of physical attack. For some, dislike results in more aggressive stances.

Body language is an important aspect of writing; I'd guess that is what this "no dialogue" assignment is about; learning to show instead of tell. You might want to rethink your choice of relationship; body language tends to be associated with stronger emotions than just being with a friend. There may still be proximity and openness, perhaps non-romantic touching, but these are more subtle indicators, that readers may not pick up on.