How do we mourn the loss of a friend?

How do we explain the inexplicable?

Grief’s many forms come to us unexplained, uncontrolled and unblemished – pure, raw and all-encompassing.

My instinct is to write, to share my experience, perhaps in the vain hope that catharsis will come through the words on the screen.

But now as I sit and write, as I try to find the words, wait for them to flow, they refuse to come.

You died on Boxing Day. I’ve been friends with your family through your sister since before my transplant when she set up an organ donation campaign at Durham University and included me in it.

I’ve shared the peaks and troughs of life with all of you over the last seven years of friendship – through the highs of getting married to the lows of losing loved ones – and your death is one of the toughest.

I try to smile. I try to remember the wonderful times we shared, like our mini-tour of Hadrian’s Wall this summer. I try to remember the laughs, the fun, the frivolity.

But grief doesn’t always give us what we want.

Instead I’m left thinking of the hole you’re leaving in your family, a family who have had to endure too much. A family of such belief and faith and certainty that I don’t understand the trials they are being sent. A family of such closeness, such togetherness, that losing another member of it is too much for anyone to contemplate.

At the same time, though, it’s hard not to feel a sense of wonderful gratitude.

I’m grateful to have known you, sir. I’m grateful to have known your wit, your views, your humour, your idiosyncrasies, the broadest of smiles, the most contemplative of minds. I’m grateful to have had chance to discuss the good and bad bits of new Doctor Who episodes as they were broadcast, grateful to have understood your passions and your passionate dislikes and everything that made you the man I knew.

Most of all, I’m grateful to the wonderful donor and their family who, when all else was falling in around them, took the bravest decision of all to grant the gift of life to a then-14-year-old boy whose heart was failing. I’m grateful that your family had nine more years to enjoy their son and brother. I’m grateful that you lived to meet your baby brother, who also left us too soon. I’m grateful that you were given enough time for me to meet you, to get to know you and to consider you a friend.

There is no escaping the sadness that your death brings, the black cloud of disbelieving grief that just wants you to drop a sarcastic comment on my Facebook status update one more time. There is no escaping the fear, the knowledge of the inevitability of something similar happening to me, that comes with transplant-related deaths. There is no escaping the reality that we’ll never hear you laugh again.

But there is no escaping the gratitude we all feel to have had our lives blessed by your presence.

And that’s what I’m going to cling to.

Gareth, sir, look after Theo, keep an eye on us and lie peacefully in the knowledge that you made our lives all the better for knowing you. Thank you.