The old saying "nice guys finish last" is a myth -- sort of. In terms of relationships, being a "nice guy" has a whole other meaning than what people think it means. It has nothing to do with chivalry and romance, but everything to do with with identity and self-worth.
Respect yourself. Respect your ideas. Have your own opinions. Know your worth. Be confident. Love yourself. Be passionate. -- These are all things the "nice guy" that's finishing last lacks. It has nothing to do with treating a woman right, but everything to do with trying too hard and in all the wrong ways to impress her.
The guy that lacks those qualities will quickly go to the friendzone.
Remember, it's not about being respectful to women. A real man will always be respectful to women (that doesn't mean he can't flirtatiously tease her), but respect doesn't mean a lack of identity and self-worth. In fact, I would argue that the man who knows his identity and appreciates his self-worth has a better ability to respect women than one that doesn't.
Be chivalrous. Be romantic. Be respectful. Be confident in yourself. -- Be a real man.
Or keep doing what you're doing and be single in the friendzone.
The choice is yours.