DS is 10, year 6.
I live opposite a gym. And I mean OPPOSITE. About 10 strides away. In fact I can see people on the treadmill when I look out my front window.
I can normally manage to go to the gym when DS is at school. However, I like to also go one weekend day (and also during half term). I have checked with DS and he is fine with this. If he wants me he can either call me and I'll be there in 30 seconds or he can even pop over. Sometimes at the weekend I'll go when he is playing out with his friends and I can see him from the gym windows. Otherwise he normally has his computer time. I go for an hour.
However, last Sunday when I was about to go, he mentioned that he looked forward to me returning from the gym. I asked him did he mind me going, was he uncomfortable on his own? He said no, he didn't mind and he wasn't scared or anything, just that the house is so much nicer when i'm at home "cos your my mum, and i just love having you around." He was saying it in a sweet way, not in a worried way.
I didn't go in the end, because I thought, well one day (soon I presume) he literally won't care if I'm there or not (or will even prefer to have the place to himself) so while he is comforted by my presence, I should make the most of it.
Another part of me thinks, don't be ridiculous, it's only an hour. And he only means he prefers me at home in the same way he prefers sleeping in my bed even though he is perfectly capable of sleeping in his own bed. He would even prefer me to sit there next to him while he plays on the computer while giving me a running commentary but I draw the fucking line there .