My sister (only sibling, we were v v close, best pals really, rented flats together etc, only 2 years apart) was diagnosed with a rare, aggressive type of cancer when she was 22 and I was 24, it was horrible. And such a shock. We all grew up pretty quickly. We had a shared friendship group and that switch from being out all the time, carefree and being daft to visiting her at the hospital was so fast and sobering.
When she died just after her 25th birthday my parents and I were bereft and it took me a good few years, in fact probably until after my 30th birthday (so at least 3 years) to be interested in dating again or looking for jobs or caring about my career.
I met my now DH when I was 31 and he was brilliant, helped me so much moving on and getting on with things. My mum died recently too, she'd been diagnosed with Alzheimer's about 10 or 12 years ago, so a few years after my sister had died. That's put things in perspective too, seeing her go through that and losing herself to the disease. It weirdly felt similar in some ways to when my sister was terminally ill, the person you love just deteriorating. Horrible. It's a clichéd thing to say, but time makes things a bit easier and also helps with perspective.
Having children too gives you a change of attitude to what's important in life. One of my children is disabled, non verbal, a lovely 7 year old but very challenging and it's hard. Day to day can sometimes be a battle. I see friends and it seems like they have sailed through their lives; still got their siblings, still close to them, lovely partners, parents still alive, great careers and neurotypical children who seem to be thriving at everything. Sometimes it's hard not to feel sorry for myself that I don't have that but then, I feel like I'm a really strong person. I don't let things worry or phase me now as much as I used to.