my three-year old male boxer

Question
Twice now, I have noticed a change in my boxer's behavior when company comes over.  Max is always excited when people come over and jumps and wants attention.  However a few weeks ago, a friend came over (who he knows# and he brought his teenage daughter and her boyfriend with him #which max never met# and instead of getting excited, he was scared. He immediately put his ears back and his tail between his legs and went under the bed. When he finally came out, he stood by my side and was not himself at all. Then, a few days ago it happened again, however with two people he has known for years.  My girlfriend and her teenage daughter came over and he immediately put his ears back again and his tail was between his legs and he would not go by them.  He was shaking.  When I sat on the couch, he came up and sat next to me #well practically on top of me).  When I got up he was under my legs and would not leave my side.  It took about 15 minutes for him to relax and act normal.  Usually when my girlfriend comes over he is so excited he is all over her and same thing with her 16 year old daughter.  Most of the times, he does his usual guard dog act, if someone walks past the house he will growl and for some reason he absolutely throws a fit when the mailman comes. I am just wondering why this unusual behavior with people he knows. I cant tell if he was protecting me or wanting me to protect him.  Now I did read that dogs are effected by house changes and my son has been at his dad's for five weeks and my daughter just left two weeks ago for her dads for four weeks.  I don't know if that has anything to do with it.  I would love your opinion on the matter. My dog, is a fun loving, never aggressive, playful boxer who always loves company except for the last two times that someone came over.  I know they never hurt him because the first visit they never met and the second one, they were never left alone with my dog to cause harm to him.  Looking forward to your answer.

Answer
Sounds complicated.

Changes do effect dogs, especially Boxers. They belong to the "family" and consider themselves a member- not a dog.

Your son and daughter leaving might have him in an insecure state- it disrupted his family and routine and he does not understand what is going on. It has made him insecure.

Insecurity can show either in his fearful behavior or in an aggressive behavior. Count your blessings- Max's is fearful.

I would recommend not having company until your kids return and then inviting your friends over (that he knows) and see if his behavior goes back to normal.

Let me know, please.