In the US, if I cannot finish my PhD in 5 years, will I lose my stipend and have to pay for my own living costs? The contract says financial support is for 5 years. I am not able to support my own living cost.
You need to ask someone in your department (your advisor, or whoever is in charge of the graduate program).  Five years is pretty good, and it's unlikely they will guarantee more than that, but departments vary in how they handle students who outlast their funding:


Some departments simply cut people off.  At that point, you have to support yourself through loans, savings, or a job (which could be an outside job or extra teaching, depending on what's available).  This can be quite a burden, and it's an incentive to graduate in five years.
Some departments will offer an additional year of funding if they can afford it and think you will make good enough use of it.  It's not guaranteed, but it might happen if you need it.
There may be other sources of funding, such as your advisor's grants or a dissertation completion fellowship.  Whether this is feasible depends heavily on the field and your personal circumstances.


There's no generic answer, and nobody on the internet can tell you which of these cases might apply to you.