M.L.
Hi, L.:
I'm also a full-time stay-home mom with a nearly six year old daughter & a 3 year old son.
Congratulations on your baby girl!
My guess is that the changes you've seen in your little boy's demeanor are likely ENTIRELY due to the MAJOR changes going on in your family's lives: pregnancy/sister coming and stress resulting from your dad's accident. The fact that he's been your one-and-only for SIX years and will soon have to share you with a sibling is HUGE. No matter HOW joyful you are about the baby, think of all the questions & uncertainty that no doubt overwhelm you at times when you wonder what it will be like to mother two ... then imagine what's going on in HIS mind!
Kids are so much more perceptive to even subtle changes than most of us adults. They absorb everything but then often don't know how to express the resulting anxiety or confusion they feel.
I find that sometimes their feelings come out in unexpected ways (on the surface it may seem like 'what do soccer and homework have to do with becoming a big brother or dealing with concerns about grandpa?'). I'm certainly no expert -- just learning as I go and trying to do my best for my kids like we all do -- but I suggest setting aside some time each day that is ALL ABOUT HIM (even just 15 or 20 min/whatever you can manage). Let him feel like he's your sole focus during that time: whether you're taking a walk together, reading a book, tossing a ball, baking a batch of slice/bake cookies, going for a milkshake, skipping rocks ... whatever he enjoys. I don't think it matters much how you spend the time just so he feels like the only thing that matters to you is being with HIM.
Maybe once a week you can plan an outing or activity -- again the focus being time for HIM. Don't we ALL love having something to look forward to, whether it's a vacation/party/sleepover/date night/movie night/or just a couple hours of mommy-time-out? I know I do.
Maybe it seems I'm over-simplifying, but who knows? It could make all the difference. For both of you! (Don't mean to exclude your husband, but I'm guessing he's gone a lot with juggling his music and school.)
On top of whatever you do, I'd make sure you're giving your smart, perceptive little guy EXTRA hugs, snuggles and reassurance that you love him and are proud of him NO MATTER WHAT -- just for being him.
I hope this is helpful to some degree.
God bless,
Julie