This is a very nuanced and detailed argument, but I’m going to keep it as simple as possible for the sake of this post, even though it isn’t that simple. This should, just about, cover it.
Theists love to throw the word ‘true’ and all its derivatives around. They like to claim a special privilege to truth in and of themselves and often beg to those who don’t believe to ‘seek the truth’ or similar, patronising phrases.
The problem here is that when an atheist speaks of truth, he’s generally speaking of what is objectively true while when a theist speaks they’re generally talking about what is subjectively true for them.
There’s a difference between ‘I believe in god’ and ‘god exists’ and this is where the disconnect comes.
It is subjectively true, to me, that I don’t like the taste of courgette. That doesn’t mean nobody else can like it or the courgette is necessarily disgusting, it’s a matter of taste.
It is objectively true that when I drop something the Earth’s gravity will pull it down to the floor at my feet. This is true.
When a theist says ‘I believe in god’ we may as well take them at their word, there’s no real way to tell whether that’s true or not (other than, maybe, an MRI machine or a lie detector). When they make an absolute and objective truth claim – ‘god exists’ – we need more.
We can easily and repeatedly confirm the existence of gravity by the evidence. The same goes for so many other things that we can say – and show – to be objectively true from the existence of an object to the fact of evolution.
If you want to claim that something is TRUE, that’s what you need, evidence. If you could show your god was true, I – and other atheists – would believe.
Reality is not subjective, what is true must be able to be shown to be true. That something is ‘true’ to you, does not mean that it is actual, real or true in terms of reality.