my BFF has been being weird about me dating. She actually said I was imagining a guy was flirting. And I was trying to tell her we had had two dates already, but she interrupted me to tell me I was seeing things that weren't there. (Two dates is not my imagination....)
It may be jealousy (that you are dating cute younger men) or jealousy (that you are spending time with men and not giving her as much attention) or it may be discomfort. My best friend is youthful, attractive, could easily date men 10-20 years younger - but she has this deep-seated fear that if she dated a younger man, or a very handsome man, he would leave her eventually for someone younger or prettier. All fine and well for her- but when she sees ME with a younger man (and current guy isn't that much younger, just 7 years, but he's super-fit and gorgeous) she projects HER fears onto ME.
Singing along to the radio is a good trait! I like guys that are not so full of themselves that they can't be silly.