"Can a pup also be boy and friend to his Handler?"
i think a lot depends on the kind of pup, your definition of 'boy' - and the mental space you bring to your play. BUT - i would definitely say YES!!! because that is the relationship i have with my own Handler: i am His pup at heart, but i am also His boy *and* His friend - after 5 years of playing together, how could i be anything less?
Think about owning a *real* puppy - as it's owner you become the leader of it's pack, it's Alpha: you must establish dominance over it in order to teach it, but that must be done with a loving and friendly hand. You don't break a dog's spirit: you nurture it, you guide it. Teach a dog to obey through fear, and one day it will turn and bite you; tame it, befriend it - teach it to Trust you, and you have a faithful companion for life.
A dog obeys You, is *devoted* to you - it follows You anywhere and will do anything for You - because it loves You, because as it's leader you are the centre of it's world.
Being a pup is a bit like that. There is an openness in You - a kind of yearning to be able to give yourself fully and without fear. It's a kind of vulnerability: you doubt yourself, your own strength and worth - and you naturally seek others who will help you find that strength you lack; You seek assurance, guidance, protection - and Your Handler gives you that. When given with a gentle caring hand, you cannot help but love Him - it's in the mind set.
That vulnerability seems to stir deep feelings of protection and guidance and nurturing in the Handler in turn. The more fragile the pup the deeper the urge to protect - a flow of power between opposites: Your Yang to his Yin.
*Any* consensual BDSM related relationship has an element of that - it's the power play of submission and dominance, surrender and protection that creates TRUST, that fuels our play and creates that intense bond between players over time. But i think it is stronger in those relationships based on 'relationship' rather than 'possession': Sir/boy, Coach/student, Daddy/son, Mentor/mentee - Handler/pup... (but i do think that pup's generate it more than any other form of 'submissive' - it's what makes them a pup rather than a slave.)
MY Handler describes a 'boy' as a playmate who never fucks Him. They yield to Him, but are not lesser than Him. It's a useful mind-set - it means that even whilst He is always dominant, we are still emotionally equal: both know the other respects and loves them, and would never do anything to hurt them.
That builds an incredibly deep Trust - and creates a genuine friendship.
But being a pup is only one part of who i am - who *any* pup is. Likewise - a Handler is more than just a Handler. Those titles - those 'roles' - are labels that help us understand some of the interplay between us - they are names for part of our identity - and ways of thinking about our *relation* between each other. Different interplay requires different names - different models. And so i am sometimes purely 'dog', other times 'boy' (even occasionally 'Tech-support' or 'Research-pup' ;)) ).
When my Handler needs/wants a dog - i am His dog: proud and happy to release myself from all thought or embarrassment - curious and eager to explore new games, to romp after a ball in the garden, to sit at His feet quietly whilst He works or chats with friends - freed to release the vulnerable part of myself to His protection and control.
But sometimes He needs more than such simpleminded companionship: a dog can be fun, but it's lack of opposable thumbs can be limiting... ;) it's also difficult tying a dog up properly - or getting them to express their emotional needs when all they have is a limited range of woofs and growls...
And so although i always wear His collar, and am at heart His pup - i am at times also His boy, His fuck-buddy, His urinal, His pillion, His confidant - just as He will be my advisor, my Mentor, my friend.
That friendship is based on 5 years of playing and talking, sharing time together and common experiences. It extends and is deepened by our shared love of bike rides, meals out, little trips, shared jokes... It's a friendship that is also deep enough and broad enough to take in our sexual play, my submission and respect, His dominance - but only because all of those are also based on mutual respect, care and Trust.
But then - isn't that so for *any* genuine relationship? Even if one of us proudly wears the Other's collar...?