Leo and Aquarius are opposite signs. The difference can attract them strongly and later reveal its difficulties in life as a couple.
Aquarius values their autonomy and, when they feel someone is trying to organize their life, may react like a teenager protecting their freedom. Leo enjoys leading and may read that resistance as a lack of willingness to build a life together.
They may also differ on social protocol. Leo usually values good form and recognition from those around them; Aquarius may enjoy stepping away from what is expected and breaking with convention.
The other affinities in the synastry can offer points of support. What drew them to a different person needs to keep its place once it is no longer new. The bond can wear down if it becomes an attempt to correct the other.