Is it normal to have threesomes often?

I had always been a good girl until I turned 16. My first boyfriend was hot, hot, hot! I knew he was the guy I wanted to give it to. So one night, my best friend (lets call her Mandy) and I were smoking a couple joints, and finally my boyfriend came over. He had brought a case of beer for a party that we would be going to. So were all sitting around, jamming on the guitars and on the drum kit, when we decide to have a smoke/beer brake. Now me and Mandy used to practice kissing each other when we were younger lol. I playfully gave Mandy a kiss on her cheek, then on her lips. My boyfriend thought it was hot. Anyways, by the end of the night, I was not a virgin anymore, and had just had my first threesome. Fast forward 2 years, I meet this super hot older women at my place of work. She is 10 years older than me. We hang out where I work, do dinner together, go out for a drink, etc... One day she takes me to the stag shop to help her pick out outfits that we think her boyfriend might like on her. It was fun, and she has AMAZING tits (as I helped her dress and undress etc...) later that night at 3 o clock in the morning, she calls me and says a cab should be waiting for me outside my parents house in a few minutes and to be ready to go. Besides the usual drug use, I was not prepared for what I met at her house. I open her front door to a big, wet kiss on the lips from her (hot!) and she leads me in to her house. BF is sitting on the couch watching t.v, she tells me she just has to shower quickly. I follow her upstairs, we enter the bathroom. We smoke a joint, snort some blow, and then she gets naked and gets in the shower. we talk about tattoos (we're both heavily tattooed and pierced). I show her my 'private' piercing (it's a 00g, I can fit a sharpie marker through it) and she thinks its the coolest thing! She asks me if I would show it to her boyfriend. I say yes. More drugs, then we head downstairs. More or less, me showing him my piercing, led to some petting, kissing, etc.. you get the idea! Fast forward 2 more years, she's broken up with her boyfriend and we've already lived with each other for a year. We have a super good relationship that works for us. We like to fool around with each other, but when we need a man for a night, we call a (very hot!) mutual friend that will spend it with us. the rest of our relationship is just us. It really works well for us, we get along, no real problems, etc... We have threesomes about once or twice a week. I'm only 21, and have had more threesomes and foursomes (with the same people more or less) more times than I have fingers and toes!Is this situation more common than I think?