You know something I have realized... When people compliment you on your long marriage, they are not saying "Wow, you managed 19 years of beautiful bliss marriage! How awesome!" They are saying "Amazing, because I know you have weathered some storms, because all marriages do. Hats off to you for two imperfect people keeping a commitment".
There is not one long marriage I know that has not had its trials. Maybe it wasn't infidelity, but it has been something. And now, when I look at couples who look happy and have been married a long time, I wonder to myself what hardships they have faced together? Is it infidelity, poverty, addiction, divided families, health crisis', etc? I know these people have all faced very hard times where it would have been easier to leave.
So, when they compliment you on your long marriage, you truly earned that compliment. You are weathering a storm, and still trying to keep your commitment.