I made the same mistake, BUT... DL should not be the only source of learning French. Check out this link: http://www.collinsdictionary.com/dictionary/french-english/belle?showCookiePolicy=true then compare senses 1 and 3. Outstanding question for me: How then would one say in French: "the roses are nice"?
Technically, yes. In IPA terms, mais is /mɛ/ and mes is /me/. It's a very subtle difference to my ear but you can hear it if you try each word by itself in Google Translate. The way I would describe it is that mes is almost like the English word me, or like may said with a Scottish accent, whereas mais is more like an American saying may.