Wouldn't it be great if everyone got along, specifically your parents and your fiancé? But no, get them in a room together and the mood gets dark. They've always been cool with him but now that you're engaged, mom and dad's attitude is downright frosty. What's sparking your parents' disapproval? They may not like his profession, lack of a big bank account, or politics. Or his personality. And he doesn't like them because well, they started it. Here's how to survive long-term without losing your sanity.
Accept that they may never get warm and cozy.
In a perfect world, your mother and father would consider your fiancé not just their future son-in-law but their future son, but that's not going to happen anytime soon. As hard as it may be to accept the situation, it's reality, so it's better you get used to it now than pretend everyone gets along.
Don't play peacemaker.
If you've tried to assure them that they've got nothing to worry about but they persist, drop it. You won't win if you constantly try to prove to them what a great guy he is. They've got to figure that out on their own, which will hopefully happen one day. For now, though, they've put up a wall and have no intention of knocking it down any time soon. So throw down your hammer and leave the wall alone. If you repeatedly try to demolish it and fail, you'll only stress yourself out.
Try to understand the problem.
As bad as your parents' behavior is, it probably comes from a place of love. They may be acting out because they are worried about your future if, say, your groom is in graduate school and you'll be the sole breadwinner of your new family, or there's a big age gap between you and him. Those aren't excuses but possible reasons for your mom and dad's bad attitude.
Keep them apart at get-togethers.
Your parents and fiancé will have to be in each other's presence at the wedding but, fortunately, other family and friends will act as buffers. Postwedding, it's more challenging like during holiday dinners and other family celebrations where the body count is less plentiful. To avoid any unpleasantness, make sure they're not within spitting distance of one another—put lots of physical space between them, such as seating them at opposite ends of the dinner table.
Stay calm and confident.
If you're happy with your relationship with him, and are certain your parents' objections are unwarranted, don't let their negativity dominate your world. It's your life and you get to love whomever you choose, with or without your parents' seals of approval.