Can I lose custody because I do not have a job?

Not just for that.

If you don't provide a home, do not provide proper food, or send them to school.

Also if they file using good lawyers for all sorts of reasons and you can't afford an attorney often they may win because they had more expensive attorneys

Can I lose custody because I do not have a job?

No. But you can get more child support and if married or formally married more spousal support.