Synastry - The Astrology of Relationship
Each Zodiac sign is one of four elements, usually fire gets on best with fire and air; air gets on best with fire and air; water and earth get on best with water and earth.
The whole question of what works well together depends upon what you want of each other - what is your purpose in being together, and also where each of you is in terms of personal evolution and maturity?
There are indeed times when a cosy, harmonious relationship would be a dream come true - but more frequently we have a challenge to deal with and it may be very helpful to work on it with a partner who is challenging.
Also it is very simplistic to compare Sun sign with Sun sign and nothing more. Astrology itself is so very much more than Sun signs, let alone the complexity of relationship, so these comments about compatibility are only part of a bigger question.