That’s quite a lot to handle all at once. You have my sincere sympathy. All I can say and advise you to do is to take a deep breath, take care of yourself as much as you can after you have grieved this situation, and begin to sort out what your plans are. lDon’t make any important decisions while you are distressed.
I’m not sure if you mean he will return home, or not. However, keep the evidence and dont give it to him when he returns. You may need to show it to a lawyer or court later. Seek immediate help for yourself, be it through counseling, a friend who listens, or your family. The important thing is to regain your strength before you begin to deal with whatever comes next. If divorce to you is imminent and it sounds like it is, get yourself a good lawyer to help you with the process.
You will go through various stages of this grieving process as if it were a death of someone. Right now, support is very important, and a clear mind later to make the right decisions. Your children are suffering now and they too need support. Talk to them, tell them you are there for them, seek counseling if needed, and let them know you will all go through this together. Expect them to be angry and upset, because that is only normal. Hopefully their Dad will see them in the future after the difficult part of adjustment is over.
I wish you the best of luck.