That's because people are more than just their sun sign.
There are other planets which also affect someone's personality.
Your nostalgic signs both cherish family and tradition.
Since you don’t trust easily, you may have a small, tight-knit circle of friends that you keep for life.
A water sign relationship can devolve into a parent-child dynamic (complete with baby talk and cloyingly cutesy nicknames) and self-destructive indulgence in food, drink and self-soothing activities like shopping.
You'll find that some of these forums are generally positive in tone, and some are generally negative.
That doesn't guarantee that will be your experience, however you are very likely to recognize some common patterns which can be fascinating.
To fully understand someone or how compatible you are with them we need to calculate those other planet positions from their date of birth and then compare them to your own.
This unlocks the real power of astrology and gives much more useful and specific information, such as how they view you, how to turn them on, how to avoid arguments with them etc.