I can tell you from personal experience that affairs never end well for any of the parties involved, especially when there is also a pregnancy. The very best advice you can be given right now is something I wish someone had said to me a long time ago—be honest with everyone RIGHT NOW. Tell the truth about everything. It is the only way to avoid much more pain. This is stil going to be a difficult situation for everyone involved, but by getting the truth out now, things will be better in the long run.