K.W.
My husband jokes that our middle daughter (almost 6) looks exactly like me. At times he seems to be tougher & have a very low frustration level with her than my eldest (7) & youngest (3 1/2) who, incidentally, look exactly like him.
Family dynamics are always muddled -- biological or not. And I always tell my children that we were planned to be together from Heaven. Whenever my eldest becomes annoyed at me, my husband, my other children, I tell her that she agreed to be a part of our family from Heaven, so she needs to find a way to love us despite our flaws. We were meant to live, grow, and thrive together as a family in our house (wherever that house is).
Although my eldest is only 7 & we haven't hit the middle school years, I've taught children at that age. Children of all ages are intuitive & will play on our fears -- without meaning to. Your son is 11 years old and asking for alone time with mom. There is nothing wrong with that AT ALL.
However, on his Birthday -- I think there is something wrong with that. Obviously, he is annoyed with his dad for one or a multitude of reasons. Not inviting his father (who is in all sense of the words -- his father), is pretty insulting. "Take that dad." The words "family family" should bother you.
God has put you all together as one family & there should not be levels of "familiness." Just as my husband seems to favor the children who look like him over our one child who looks like me, it is unacceptable in what God has ordained as our family. Husbands, mothers, we need to examine what we say & do and if we unknowingly contribute to the situation. My 7 yr. old has taken to "listening" too well to our adult conversations. Not good.
I think for the well-being of your entire family, you need to spend one-on-one time with your 11 year old son, but not on the day he was born. That would most definitely solidify the normal rift between a pre-teen & his father. Also it won't do well for your relationship as husband & wife either.
Birthdays should be celebrated with family. However, that being said -- since your other son is quite young & won't really be aware of who is going where -- have you ever thought of having your 3 year old stay with grandma, and you & dad focus all of your attention on your 11 yr. old? That would be a thrill for him -- I think. And since your other son is 3 - -he won't really know what he is missing if grandma gives him ice cream & he plays all day. (If your other son were older -- I would never suggest such a thing -- because all the family should celebrate.) Also, since it is your son's birthday, I"m sure dad will try harder to increase his threshhold of tolerance.
Sometimes we get into patterns of immediate responses & a special day or outing might jar us out of that normal, daily dance or social pattern we have with our children.
Have your son choose another day for alone time. Talk to your husband privately about him spending alone time & cutting out the sarcasm. Sarcasm is meanness veiled in humor. The reason your husband uses it -- probably -- is because his dad used it on him. And, please, do not mention that your son wanted alone time with just you on his birthday - but alone time with "his parents." Men are hurt by what children do & say, but they are better at covering up their hurt.
Are some of your difficulties because your son was 7 when his dad stepped into your lives? Of course. But that doesn't change the fact, that God has planned it all out that way, and your son should know that. He's stuck with his present Dad & both of them sound as if they need alone time -- desperately.
As moms, we need to help our husbands (sometimes) by getting out of the way. We need to set the stage for a social outing with one child & then let the relationship go as it will.
There will be high points & low points -- but you -- the mom -- should be a catalyst to encourage positive experiences -- not a third wheel. I strongly encourage you to have your husband read Dobson's book about Bringing up Boys or another book where the author talks about the pre-teen boy. If your husband refuses to become educated about his rapidly growing son, then you read it and condense the material. Since your husband sounds like a good guy, any father would read a few pages of notes on how to have a better relationship with his eldest son.
(And as the mom, you have to live, think, breathe the fact that you are all together under the guidance and will of God -- and stop mentioning or even really -- thinking -- that because no blood is shared -- this should affect the father/son relationship. Your son is smart; in very subtle ways he has picked up this way of thinking & you have to correct him on it.)
I hope I wasn't harsh.
I find that, personally, lately, the mom (me) makes things worse when I over analyze a family situation. But when I really listen to what God seems to be telling me & unite with my husband on common ground, everything makes more sense & seems more clear.