Ok, you need to split everything up. First off, you need to leave your relationship of 25 yrs, not because of another person involved but in deciding what is right for you. Don't get the two mixed up. Being with another person needs to be because you truly want to be with that person, not because you need to get away from the other one. See?

The other thing you need to look at.... staying for the sake of the kids... hmmm... are the kids going to be happy with an unhappy parent? They won't thank you for being in a miserable relationship, that is for sure. They won't thank you for leaving either, so bear that in mind too. Children need happy parents whether they are together or separated.