The crucifixion was an inner and symbolic experience, and the beloved one leaning close is the faculty that rests against the source of divine nourishment. The breast is the place of that nourishment, and to lean upon it is to draw awareness directly from the higher mind, which is what Lord names within a person. Peter turns and sees this closeness following him: the practicing self recognizes the part of itself that stays nearest the inner supply, fed straight from the center rather than reaching for it from a distance.
The part of a person that stays closest to the higher mind is fed directly from it, resting against the very source of inner nourishment.
Breast: the place of divine nourishment against which the awareness rests
Lord: the higher mind within a person