She told the new issue of Britain's Elle magazine: "When I was dating a guy I was hiding everything that I did because everything personal felt like it was immediately trivialised, so I didn't like it.
"We were turned into these characters and placed into this ridiculous comic book, and I was like, 'That's mine. You're making my relationship something that it's not.' I didn't like that.
"But then it changed when I started dating a girl. I was like, 'Actually, to hide this provides the implication that I'm not down with it or I'm ashamed of it, so I had to alter how I approached being in public. It opened my life up and I'm so much happier."
The Equals star recently insisted she doesn't want to define her sexuality.
She said: "Me not defining it right now is the whole basis of what I'm about. If you don't get it, I don't have time for you. There's acceptance that's become really rampant and cool. You don't have to immediately know how to define yourself.
"I had to have some answer about who I was. I felt this weird responsibility, because I didn't want to seem fearful. But nothing seemed appropriate. So I was like, 'F***, how do I define that?' I'm not going to. Plus, I didn't want to f*** with other people. I didn't want to be this example: It's so easy. I don't want it to seem like it was stupid for them to have a hard time. I find the movement that's occurring to be so important, that I want to be part of it."