Cheat or ask for open marriage

My wife 42 and I 42 have been married for 18 years. She has been declining on her sex drive over the years. Mine has stayed the same. It's been frustrating. In the past we have sex talked about other people but she has mentioned it will never happen. In the past I have had a few short term hook ups and they were fantastic while they lasted. I'm not getting any younger and want to explore more. I have been snipped so I'm not worried about any accidents. It's been a huge frustration for me over the years. I'm growing tired of waiting. What are your thoughts on cheating (trying to keep it under the radar) or to ask for an open relationship which will most certainly end in divorce.