Why do people not see me as being his wife even after 20 years?

Maybe I'm making a big deal over nothing. I've been married for 20 years. We have a 16 year old son together. DH was married before for 2 years back in the early 80s. The girl he married was 19. She already had 3 children of her own (4, 3 and 2). DH and his ex dated 3 months before they married. DH adopted her kids and the ex promptly left and filed for divorce. He raised the 3 kids on his own. She divorced him and went on with her life. He did everything on his own with no help from her. She didn't even come around until the youngest turned 18. The kids have forgiven her for not seeing them all those years. Still to this day, people think of DH's family as his ex wife and her 3 kids (which legally are his). I'm looked upon as being like some random girlfriend, mistress, friend or something. I've never done anything wrong. DH's kids and myself have always had a great relationship. DH's family still call me by his ex's name, when clearly I'm not her. DH's sister still randomly talks about how pretty or nice his ex was (nice enough to marry someone, use them and leave her children). DH's family does not include our son in any family activities, but will include DH's adopted children. They even include DH's adopted son's girlfriend's kids, but not me nor our son. It's always been this way. It's like they see me as DH's mistress, and our son as just mine and he means nothing to them. It's not like I broke up their marriage. She left in the early 80s. I met DH in 1990. One niece is getting married. It's a casual affair, but they only asked DH and his 3 adopted kids to attend. Not me. Her mother is now friends with the ex on facebook and invited the ex to the wedding, but didn't invite me. and worse yet, didn't invite our son. Maybe his family is just weird, but it's beyond annoying. I've inquired and was totally ignored. It's not only his family though who do this. I can't tell you how many times DH has run into a former coworker or neighbor or something at the store. When he says I'm his wife, they think I'm his ex. Everyone clearly knows what she did to DH. Maybe they think he remarried her or something. DH doesn't think it's a big deal, but he's not the one who has to live with it. He's never thought it was a problem that his wife of 20 years and our 16 year old son are considered outsiders and never included in anything by anyone on his side of the family. DH will even go alone to his family events without asking myself or our son to go. My son and I end up doing things together instead. My family and friends adore DH and his 3 kids and treat them like family. I can't be the only one this is happening to. It sucks. I feel like moving away. It's easy for someone to say to just get over it, but it really, truly sucks. Had I known that I'd be shunned after 20 years of marriage, I honestly don't know if I would have married DH. Is anyone else in this situation? Any advice?

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