Your son may need more attention than many 11 yr. old boys. That's okay, he has a history that I presume would require extra attention from (you) his new parents. From you he's learning to interact. Thankfully he's likes the interaction (and likes you and your husband.) This interaction builds his communication skills and builds trust and an ability to relax enough to have fun. Him trusting you, is a gift, that money can't buy.
I know you are new to parenting and suddenly this child is sucking up all the time you have. It's exhausting! You have every right to be tired. All good Mothers know, being weary comes with the territory. Slow and steadily you can wean him off of his complete dependence on you and your husband.
With toddlers and older kids, I've used and recommended saying to your child, "Mom need 15 minutes or 30 minutes to work on the check book." "I'll set the timer and when the buzzer goes off I'll play a game of ____ with you." Then do it.
He doesn't always have to play a game. He can help you and learn by helping in the kitchen. To start, he can learn to shred cheese, peel a potato or carrots, wash the celery or stir cookie dough or brownie mix. Stand him up at the kitchen sink with a potato peeler and potato, show him how to use it. The peels may fly, that's why I recommend you use the kitchen sink as a prep area, it makes clean up easier. Put a bath towel on the floor in front of the sink. After you're finished prepping food you fold up the towel and shake it out the back door. Then throw the towel in the laundry hamper.
Work together, he can help you dust the furniture or use a dust mop on solid surface floors, then he can dust bust, the dirt pile. My kids liked it when I'd turn on music and we'd do a couple minutes of loud (if you & he like it loud) rock & roll house cleaning. Rock out, as you work together.
It may take a while for him to find something that he can do alone, or anything he likes to do alone. Eventually, he may like Lego's or Kinect's (those metal building toys.) He could become an avid reader. Has he tried drawing or painting? What about puzzles? He may want or need to start with easier puzzles, Lego's and paints before he can discover if he likes or dislikes those activities.
My sister & her husband adopted 3 siblings from ages 5-9. Although they had been well fed and had a safe house to live in, they weren't living a full life. Prior to bringing the children home to live, my sister learned the children had no memories of playing a board game or having a story book read to them.
2 years later they are caught up to their age level (and then some!) They love to bowl! They love ping pong! The boys aren't thrilled with reading, but their little girl reads everything in sight.
I wish you the best! And I wish you a quiet coffee break, soon!
A.