Blood isn't everything. The ex's mom was a decent person and treated you well. Blood relatives don't always do that. Sometimes they're so awful it even makes sense to go no contact. Sometimes their actions are literally criminal. On the flip side there are friends that are basically family and people who adopt.

What you felt with the ex's mom was real as anything. Don't listen to people who say otherwise. The blood relatives who said it was fake were being manipulative or saying something based on being manipulated.