Divorce and remarried. Not namedropping Henry there was weird, considering all the name drops they did have.
Just like skipping any Wally mention was.
They probably haven't met Wally-2 at that time yet, if he even exists.
I don't think the divorce angle would work since Barry-2's mother was going to celebrate her wedding anniversary and the phone's speed dials didn't really hint at any remarriages.
The Flash writers like to build up a character as an ally before they twist the knife. Henry just hasn't been given enough screen time for it to make sense.