What a great step-mom you are!

My parents have been together 39 years, and I didn't have to deal with a "broken family" or "steps" until I ended up with my husband. I have a friend who I am close to him and his son. Watching that family dynamic confuses me. My husband had to explain to me the spectrum of how those relationships work. How lucky is your husband and step-son to have you willing to open your heart!
It's scary, no doubt about it!

Is your husband willing to go to family therapy with the 3 of you? It may be a good idea to have your step-son see one on his own and look into the possibility of medication. My oldest was diagnosed as Inattentive ADD this past summer, I suspect my youngest is ADHD (both girls, 9 and 6) and I was diagnosed ADD last month. I am lucky in a sense since I am going through stimulant therapy and therefore "check it out" before I decide if we are going to put our own girls on medication. There are two schools of thought, that meds are good or that meds should be avoided at all costs. I usually run down the middle, if it works great, if not, that is ok too.
This is a big, life changing event. It's normal to be anxious. When being anxious starts interfering with your life, it's time to get help. You may need it short - term, you may need it long term. Seek out a mental health professional. They can recomend a doctor if medication is appropriate, but also provide behavioral therapy to help. They may also have support groups or referals to support groups. (Of course you have support here too!) Sometimes hard issues are easier to deal with when you have others going through the same thing.
It will be hard, and some days may seem dark. Just know when you need to take care of YOU. Mom's have a habit of forgetting we need to take care of us so we can be healthy (physically and mentally) in order to take care of others. Think about riding in a plane, they always tell you to put YOUR oxygen mask on first, then the child's! If I can help, please let me know!
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I am not a medical or mental health professional, nor do I play one on TV, I just talk kinda like one!
Blessed are the cracked for they let in the light!
They say I have A.D.D. but I think they are full off...
Oh look! A CHICKEN!
Be careful how you look at the world, it may look back!
How do you want to be seen?