Dewey and Webby were best friends, but not everyone believed that.
Many people in Duckburg (and especially those who lived in the mansion) believed that they already had a relationship, they were only best friends, but do not forget feelings.
They were both in love with each other, but they were too shy to realize it, you know, you are afraid that all your friendship will collapse.
The one who feared and was most frustrated was Webby.
When the triplets and Donald moved to the mansion it was the first outside contact with boys for Webby, they were the first boys she knew, since Beackley wouldn't let her out.
They were just "friends."
But who would believe that lie?
The triplets, Beackly, Scrooge, Della and Donald no.
How would they believe that lie?
They knew them, they were their family, and when they left, everyone started talking about the beautiful couple they made.
Although they were not yet a couple, they were very close, they were not just "best friends"
Dewey wasn't going anywhere without Webby and Webby wasn't going anywhere without Dewey.
They didn't mind this, in the end they liked to spend time nearby.