When you come out to them they will likely initially be upset and even angry but it is better to tell them the truth rather then them either finding out by catching you in the act or from a friend. Rather then prolong the lie it is best to just tell her. I can only imagine that it must have been extremely difficult to except your sexuality yourself, but you have to be who you are. It is hard to tell the wife that you were unfaithful and that you can not control your feelings anymore. There is also a risk the wider family will turn against you. This is more likely because of the upset and the secret, rather than your sexual orientation.
You have a very difficult decision to face. I cannot tell you what course of action to take only you can decide and if you need help maybe talk to a support group or someone who has come out to the wife after years of marriage.