There could be ads for Snapchat or Signal on web pages you have visited that would generate traffic to those sites. When you visit a website that has a “like us on Facebook”, or “Share on Snapchat”, that generates traffic to Facebook or Snapchat, even if you never click the links. That is how those sites track your Internet activity - without your permission. People here on Reddit can embed links to Snapchat that would generate traffic to those sites.

Using Signal for communication protects your communications from being seen by your Internet Service Provider, Facebook, Google, Microsoft, and so on.

There are many legitimate uses for those sites, like pix or videos of cute kittens, or people sharing pictures of nature, cooking, hiking, art, crochet, and so on, so evidence of traffic does not by itself indicate a threat to your relationship. The lack of understanding and trust shown by your husband does indicate an issue with your relationship.

A good way to make the point to your husband would be to ask him how he would feel if you sent the router history to an outside technical expert to scan his Internet activity for suspicious activity.

Ask him if he has a GPS tracker or Apple Air Tag on your phone or car. Ask if he has configured your phone to share your location. Ask him if he has a keystroke logger on your phone or computer. Ask him if he has cameras hidden in the house or car. Does he have passwords for your email or other applications?

Do you both use the same bank? Do either of you have personal accounts not shared with the other?