Hi. I'm 35 and the mom to an 8yr old and 2 yr old. Neither were planned by me, but now that they are here, I wouldn't change a thing. In my mind every Mom is a single mom. We are the ones that get up in the night, sit with them when they are sick, get them to the babysitter, etc.
You say that you are adopting, but not what age - a baby, an infant, toddler, older?
Being a mom is wonderful; tiring; special; worrisome; rewarding; and stressful all at the same time. Since you are a first time mom, I my advice is to hang out with friends that have young kids. Stay overnight at their house, see their routines, babysit their kids, etc.
Becoming a mom isn't about what you lose, its about adjusting your lifestyle willingly to include another person, and loving that person so much that you adjust your plans for what is best for the new person... waiting to go shopping because baby needs a nap, or running errands right after breakfast since baby will be happiest then, meeting friends for lunch instead of happy hour.
As for losing your free weekends, my advice is to adjust your 'me' time to the middle of the week. Take an occasional day off from work, find a babysitter for the baby, and have your 'me' time.