Expecting first child...problems with stepson

I am due with my first child in February. I have a stepson who is 11 - his father and I have been married 4 years and I am his first wife. We tried for 3 years to get pregnant so this is a very exciting time for me. However, my stepson is way less than enthused. He actually can be very hateful and mean when we mention the baby. My sister in law (husband's sis) had a baby 5 months ago and my stepson wants nothing to do with him - mostly ignores him. Which I guess is fairly harmless, but it's not the atmosphere I will want in my home. My stepson has been an only child thus far, so I know it's going to be an adjustment for him. It just really hurts me when he acts so rude/mean/disinterested. Any suggestions??

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