This one shall be on my pet subject of many years now, and it is on solitude and loneliness (critically, their differences). I have written quite a bit on this topic over the years, and I have somehow become decently acquainted with these two words over the many times I have penned my thoughts down on them.
Perhaps you would disagree with me, but I see solitude as a state and loneliness as an emotion. Why do I say that? Well you can do things and live your life in solitude, and it is solitude rather than loneliness if you do not feel the void or the emptiness as you go about your every day.
You can certainly say loneliness is a state too, but it is not so if it is not cemented by the intensity of the aloneness that you feel. Fundamentally, loneliness can be referred to as a state induced by the feeling of emptiness or a deep desire for affection and interaction; if simplified, it can also be viewed in its naked light as that very feeling itself.
On the other hand, solitude is more of a choice that you make with regards to your lifestyle and the way you conduct your life. You may like to do things alone, be alone, live alone, and go about your every day (largely) alone; this is a decision you make and has no resultant or accompanying emotion (yes of course emotions are always present, but you get what I mean).
As such we can see solitude as a behavioural pattern, while loneliness is a feeling that may or may not accompany this solitude. Given the innate nature of humans as social creatures, it is not wrong to say that all who live in solitude will experience bouts of loneliness once in awhile (with the duration and intensity varying from individual to individual and from circumstance to circumstance), but it is not however true to say that those who are lonely experience states of solitude since loneliness itself is not a choice.
Solitude is a good thing: we all need time alone with ourselves to better acquaint us with who we are as persons, to better know our natures. The same cannot be said for excesses of it as it most likely would leave a person starved of interaction and affection. Loneliness on the flip side, in any amounts of it, is not ideal as it is firstly a very painful experience, and it could also lead an individual to do things which may have adverse effects on himself or those around him.
It is good to know the differences between solitude and loneliness. You can then assess for yourself if you are actually in a state of solitude, or if you are using it as a disguise to mask the loneliness that is lurking deep within yourself. Kudos to you if solitude is your preferred way of life, though it is also prudent to acknowledge it if you find that what lies behind it is just a wardrobe of lonely bones and hidden woes.
Are you enjoying your solitude, or are you unbeknownst to others drowning in loneliness? Take a moment to find out for yourself.