Originally Posted by JessiesGirl

You're in a space that could break several ways. He may be placing himself in front of your out of nervousness (backing up to you is a sort of reinforcement), he may have some resource guarding, or he may be simply trying things on as he matures.

The big sign to me that my dog was getting a resource-guarding issue was that she would put herself between any person or dog she knew and ANY new person, dog, object, etc. She may have only recently met them, but now she decided they needed protection. It could have been as simple as a dog she met at the park for 10 minutes before another dog entered--she'd get between that dog and the new dog. Or she'd get very upset that a person she'd met previously paid attention to another dog. It does take a pattern of behavior to recognize this propensity.

Originally Posted by Rottiefan

This kind of behaviour is usually a calming signal, used between groups of dogs. Breaking interactions to avoid escalation. Is it possible that your dog was just a little nervy in interactions with new people and dogs, and used this behaviour to try and relax the situation. Leaning in is, too, a calming signal of sorts.

Originally Posted by JessiesGirl

Unfortunately, mine was not leaning in, although it sounds as though the OP's pup is leaning in and perhaps seeking some reassurance.