Sometimes I question my decision of marrying my spouse. I keep getting thoughts that what if I had married someone else due to my choices etc. All these thoughts make me feel low because I want to focus on my spouse and I feel like shaytaan is trying to distract me. I'm not sure what is causing this as they are a religious and good person. How to protect myself from these thoughts?

1) Have confidence in yourself and take a firm decision.
2) Combat these negative thoughts by reciting Audhu billahi mina-shaytani Rajeem and keep focused on your spouse that you wish to live for the rest of your life.
3) Your niyyah needs to be only for the sake of pleasing Allah swt
4) Remove these doubts and have clarity of mind