Oh poor you, I feel sorry for you and your wife, seems that what with your diabetes, dysfunctional family background, small children to look after, etc its all become overwhelming and you cannot see the wood for the trees anymore except for some easy way out.
But its not so easy after all, is it? You probably have a lot in common with the new female in your life, but you also have a lot in common with your wife, think about it......she is just as unhappy, so have you considered relationship counselling? It can help even if you are planning to separate, you arent forced to stay together.
Dont do anything rash, the grass may look greener on the other side, but is it really? At the moment you are thinking this other female, the fellow diabetic is perfect, but once the first excitement of a new relationship has settled, you might find the usual humdrum of every day life is very similar to what you have now.
People should never go from one relationship straight into the next, you need some space to clear your head, you obviously have doubts, hence your post, I am not saying that you need to try to save your marriage, but if there a chance that somewhere there is still love and affection remaining it is surely worth giving it more time. Maybe you are both stuck in a rut and you need some time out, can someone else babysit the children, can you and your wife take some time out and be a couple as opposed to being Mummy and Daddy for a change, do something different, doesnt have to be anything expensive, go to the cinema together, discover each other again and talk to each other about your thoughts.
Whatever you decide to do, I wish you well, make sure you achieve good control of your diabetes, you need to stay healthy.