If you are in the difficult position of being faced with the prospect of your relationship breaking up, and you needing to figure out care arrangements for your children, then do not worry. There is support out there.
The common perception is that child custody cases are universally decided in the favor of the woman, but this is not really the case. Child custody courts work to decide who is going to be the best caregiver. That could be the woman, or it could be the man in the relationship. The things that are examined include income, job (someone who works away a lot may not be able to care for a child as well as someone with a less demanding job), psychological profile, past history of violence or alcoholism, the wishes of the child if they are old enough to make a decision, and the desires of the parents.
If the mother does not want custody, and the father is a capable parent, then the courts would not want to go against that mutual agreement, and vice-versa.
Child custody can be difficult, especially if one parent is using the children as a pawn in their relationship. For this reason, it is important that you understand your legal rights. Your local citizens advice bureau will have child custody resources to help you understand what the law means, and how best to approach the case. They can tell you what you should and should not do during the separation, to help your case as much as possible, and mitigate any damage that might be done to your relationship with your children. At the end of the day, the most important thing is your kids, and making sure that they still have happy memories from both parents.