Will 500 calories a day affect my metabolism? Is it a good idea?

I’ve been eating only 500 calories a day to lose weight, my friend noticed and told me that it’ll effect my metabolism and that it’ll be harder to lose weight, is this a real thing?

I have no previous knowledge, I lost 70 pounds so far but I want to lose more, I used to exercise at the beginning but since it’s summer now I hate getting all hot and sweaty, I try to work out every now and then but I end up having the worst headache from the heat.

I have been eating a single egg with piece of toast for breakfast and a salad for lunch but I skip dinner, will it slow down my burning rate?