Should I Stay Or Should I Go?

You aren't necessarily selfish for wanting to end your marriage. You are selfish, juvenile, and morally corrupt; because you've engaged in a long term affair while married. So, I don't think much of you. But, there is no reason you'd care. Your question needs an answer. You are going to divorce your wife. Good reasons, or bad reasons, that is what you are going to do. So, you may as well try to explore a life with the woman you've been seeing, IF she isn't married. No need to do any more to help wreck her marriage, if she is still with her husband.