Carlo, feeling lonely is ok, in fact, it is more than ok, it is essential. To be alone is a rare thing indeed but it is from that place, that aloneness, that growth happens.
If you do the looking round Europe first, as you have planned, you will find that as you are alone your observation of the outside world will be keener and you will also have the inner space to think and ponder. It is a process that may change the way you see the world, make you aware of how important the people at home are, all the things they do for you, the love they give you.
If you travel with someone else your conversations are inward, between the two of you, and you miss all the other things. When you travel alone you are open to everything new, everything that happens.
If you are staying in backpacker hostels you will meet lots of other young people travelling alone - it will be fine.
When you then do the Camino you will be more independent, more mature, more sure of yourself - so the friendships you make will be on friendship alone, not need.
So accept that you will be lonely, it is the central part of your journey - all is well . :wink: