Over the past decade I’ve watched a young boy grow up and become a daily reminder to me of just how proud his mother would have been

I remember there was an aquarium in the hospice where my cousin Billie spent the last few weeks of her life. Luis, her son, liked going to visit her there more than to the hospital, not realising what her move to a palliative care centre really meant. He liked watching the big guppy in the fish tank kiss the glass when he pressed his face up against it. He’d kick a football down the corridors; seven years old and often straight from school in his too-big uniform, polished black shoes loudly slapping the lino as he ran to her room.

I call Luis my nephew because Billie was always more of a sister to me. Throughout her six-year illness – she was diagnosed with a brain tumour at 26 and died at 31 – I helped look after Luis. He was just two when Billie had the first operation and although she did her best to carry on as a young working mother (she was a really in-demand makeup artist), I know she appreciated that family and friends babysat when we could.

One evening, not long after that life-changing diagnosis, I went over to Billie’s small flat in west London, which she shared with Luis and her best friend, Hannah. I had a cheap bottle of wine with me and was ready to ask her all about how she was coping after the first round of radiotherapy. But she didn’t want to talk about it. She asked me questions about my life – I’d just graduated and was a few months into my first job. We poured big glasses of the wine – she never paid much attention to doctors’ suggestions that she should quit drinking – and laughed so loudly we forgot that Luis was asleep.

It was inconceivable to me then that she wouldn’t survive, but as I tiptoed past Luis’s room, his name spelt out in wooden letters on the door, I had a crushing flash-forward: what if she didn’t?

His boyish and surreal chat helped me deal with my own grief

“I’ll always look out for him you know,” I said without planning to. “Like, whatever happens, I’ll always make sure he’s OK. I promise.” Billie brushed this off, changed the subject, hit play on Madonna’s Ray of Light. But I’d made a promise I meant to keep.

Today, Luis is 16. He’s studying at the same sixth-form college his mother went to. He lives with his grandmother. His room used to be Billie’s childhood room. But it’s painted blue now.

We hang out a couple of times a month and he insists I stick his left AirPod in my ear so he can play me “his music” – London drill and rap – and translate the lyrics: “So basically a trap house is where you sell drugs.” Yes, I know that one, I’ve watched Top Boy. “A Glock is a gun.” Yes, I know. “All right then, what’s OT?” I rack the somewhat patchy urban dictionary in my brain. OK Luis, you’ve got me there. He’ll explain it means out of town. Which sounds innocent enough, but given the context probably isn’t. I’ll ask in a slightly panicked but non-judgmental tone if the life described in these songs is relatable to him. “Naaaaaah. That’s not for me,” he’ll say, cringing slightly, and I believe him.

I understand why the raw desperation and anger of that music appeals to Luis. He’s not endured the same endemic hardships that artists such as Loski describes in his controversial tracks, but he knows pain and he knows injustice. He lost his mum before he finished primary school. He only sees his dad occasionally, as he lives out of London – Billie and he had split up soon after Luis was born.

“All I feel is anger,” he told me over a Nando’s recently. “I’m not like other people. I just honestly don’t feel anything except anger. I never cry.”

It was one of those conversations that came out of nowhere, and I’m not sure I said the right thing back, but I listened and reminded him he could always talk to me, and by the time he finished his burger he was telling me in great detail about some rapper who’d just got out of prison as if the previous conversation had never happened.

Growing up in west London, Luis is on the edge of “street” culture. He knows what’s what and goes to the right chicken shops with the right people, but he also lives with his 64-year-old grandma and is surrounded by a close family of arty, middle-class women: my mother, my other cousin Romy, and his godmother Hannah. He’s forever walking into the living room to find us all gabbing about Strictly, listening to the Rolling Stones and dancing embarrassingly after drinking too much prosecco. I’m confident his ability to shift between worlds and hold his own with boys on street corners and tipsy older ladies in Cos dresses and statement necklaces will stand him in good stead for life.

‘I don’t feel anything except anger,’ Luis said. ‘I never cry’

After the funeral I made regular plans to take Luis out. We did physical things together: I’d set him obstacle courses, we’d race between trees in the park, we went to climbing centres, trampolining, and crazy golf. But if I ever tried to bring up “feelings” he’d simply not engage – he was a baby really, and no child is equipped to deal with the loss of a parent. I’m not surprised he didn’t want to talk about it. Instead we’d share mega tubs of popcorn at the Imax and get lost in superhero movies. These things made me feel better too.

Playing with Luis between the ages of seven and 12, and getting drawn into his epic imaginary worlds and silly, surreal, schoolboy conversations helped me deal with my grief. He was so full of life, just like Billie, and being with him always lifted my spirits. He’d mention Billie anecdotally – “Oh yeah, I went there with my mum” – as if she was still alive. But over time, once he turned teenage, he started forgetting those small things about her and he talked about her less and less. Now, he tells me, “I don’t think I remember her at all.”

Once, when he was nine, Luis used the notebook and pen I’d bought him to write “I hate you I hate you I hate you” over and over again. He screwed up the paper and threw it at me. “I’m angry she died too,” I said. “But I love you and nothing you ever say or do will change that.”

Two years ago, we went as a family to a music festival in London to watch Romy perform with her band The xx. Luis has been dragged along to most of her gigs over the years, and while he always said he enjoyed them, he’d often be caught playing a game on his phone during one of the concert’s most emotional moments, (I mean, they were no Krept and Konan, that’s for sure), or asking when we’d be able to leave.

But this time he was older, and it was different. Romy walked to the centre of the stage to sing Brave for You, a song she wrote about her own experiences of grief (Romy lost both her parents in her early 20s), with 40,000 fans screaming and clapping for her and lightning hitting like a brilliant cliché in the late evening sky above. I noticed Luis was really watching, for once. As the song ended and ramped up into the euphoric opening of Loud Places, he put his arm round me and his grandma and we jumped up and down together, wildly singing along:

“Didn’t I take you to/ higher places, you/ can’t reach without me”.

It was the most un-self-conscious I’d ever seen him, and it made me feel that I’d kept my promise to Billie well. He was going to be OK. We all were.

Luis is a good kid. He doesn’t drink, even if his friends do. He hates smoking and won’t touch drugs. He’s obsessed with luxury fashion and will happily spend a day in Selfridges (probably the closest thing we have in common). This summer we went on our first family holiday to Ibiza, and when he wasn’t making endless jokes about how small I am compared to his lanky 6ft-something, we talked like we never had before. After dinner we lay on sunloungers, looking up at the stars and contemplating the enormity of the universe together. It felt like our relationship was shifting into something new.

Luis wears his mum’s diamond ring. It’s “dripping”, as he says (“drip” is the new “bling” FYI) and I know the time will come when he’s ready to find out more about her. At the moment, though, he’s keeping her close in his own way. Billie would be so proud.

How to be a Gentlewoman: the Art of Soft Power in Hard Times by Lotte Jeffs is published by Cassell at £15. Buy it for £13.20 at guardianbookshop.com