I got married when I was 22, and I decided to keep my last name. This was more an act of laziness on my part than anything else. I hated paperwork, and changing your name requires a lot of paperwork.
We had two children, and I gave them his last name. My last name is long, his is short, and I figured it would be easier for them on forms.
I later divorced and remarried, and once again, kept my last name. This time, it was because I had built up a career around this name. It wasn't a small part of my identity anymore: It was huge. My peers knew me by this name. I was published under this name. This was how Google knew me.
Also, I still hated paperwork.
So, for the past decade+ of my life, I have had a different last name than my children and my husbands. This should have created mountains of chaos, according to my family. It did not.
The children's schools won't think you're their mother!
My son is in the 7th grade. My daughter is in kindergarten. This has yet to happen. I haven't gotten so much as a batted eyelash when I've come to get them.
In fact, the schools are probably the best institution at getting my name right. I never get mail sent to Mrs. Exlastname. It's either to me, or it's to 'The parents of Kid Exlastname.'
Insurance will be a nightmare!
I've been on four different insurances since having children and getting married. Never an issue. All they want is our SSN's, not matching last names.
Hell, my current insurance has three different last names under it. Still, not a problem.
Then the doctors will give you trouble!
One thing I've learned about kids' doctors: They give zero fucks as to who brings them in. They never ask for my ID. When my mother took them in, they didn't ask for her ID. Hell, my husband took my son in for a shot back before we were married, and they shrugged it off, even with my son calling him 'Jim' the entire time.
As long as whatever you're doing is routine and you have the kid's insurance card, they simply don't care.
You won't be able to own anything together
I haven't bought a house, but most of my coupled friends have different last names. None of them has hit a single snag. Hell, many of them weren't even married. As long as they had good credit, they were in.
He won't believe you really love him
Honestly, this shit only came up once I left my ex. Before then? He didn't care.
And let's be honest: Freshly wounded, you look for anything that might have been a 'sign'. Had I changed my name, I bet he would have taken me closing my WoW account as a sign that he missed.