Am I right to think this isn't serious?

Listen if you haven't said anything yet, despite the fact that this has been happening for this long you marriage is in jeopardy and you'll be really fortunate if you can find a way to fix it. You NEED to address it to your husband, you NEED to confront this woman, and you NEED to stop being passive. It's the 21st century, women are not supposed to get stepped on anymore, and if you want to verify your suspicions, and I've never been more serious in my life, go see MAURY. I mean think about, he's sleeping with this woman and coming back home to you, if you sex life is still active you could be contracting STDs, now your life could be endanger. You need to do some serious confronting of the parties involved, my heart breaks for you that you're just letting this happen, speak up.