The person glowing does not realise this and doesn't understand what the others are talking about.
The glow gets brighter and brighter until it casts shadows and NOW the glowing person realises that there is a light coming from somewhere and that it appears to be coming from them. They still do not feel any different, any warmer, or ill.
The other friends move away because they are worried and don't know what is going to happen.
The glowing person follows them, so as not to be left alone - and the glow disappears. The glowing person realises the glow has gone and moves back to where they were - and the glow reappears.
They call their friends to come and see. The friends come near and step on the spot but they do not glow. The glowing person always glows on that spot but the others do not and they are unwilling to stay on the spot to see if the glow build up on them.
They camp somewhere else. They look at it in the morning but see nothing in particular. Next evening they go back there but no one glows - not even the glowing person.
They mark the spot for coming back to.
You could have several possible endings. Maybe the person got covered in glow worms? But you would have to change part of the story line above for that. Maybe there was a natural source of energy that builds up in the person, like a battery and then runs down when they are away from it? That's why they glowed when they first went back, but not the next night. Maybe they were going to be abducted by aliens and the glow was the transporter power building up? Maybe a trick was being played with torches?