Neptune in 5th House synastry’s relationships are highly idiosyncratic and tend to bear a karmic coloring full of pensiveness and lack of determination, to the point that it could be hard to say whether the relationship is a positive or a negative one.
When Neptune in 5th House synastry is negative, the relationship becomes very one-sided as the opinions or desires of one of the parties always prevail. Naturally, no constructive activity can take place here as quarrels and deception thrive, encouraging bad habits, spendthrifting, perversions of all sorts and ignoring even the basic moral standards.
When the aspect is positive, the partners quickly find common ground in intellectual, spiritual, educational, and any other kind of life activity, forming a constructive, mutually beneficial relationship. The “Neptunian” personality helps the personality of the Fifth House solve many practical issues by leveraging its intuition while the later facilitates a more effective way to embody the creative, aesthetic, and intuitional talents of its “Neptunian” counterpart.
from F. Sakoyan, L. Ecker
Neptune in 5th House Synastry Explained
Neptune in 5th House synastry can make me assign to my partner the role of the Simpleton while he or she takes themselves as the Smartass, and neither of you will know for sure who is right until the whole story plays out. Yet, you have the advantage here because, while the ascribed roles are never cut in stone, your partner may not even understand what game is being played, especially if their Neptune is not in the Fifth House of their own natal chart. On the other hand, if you believe that your partner is playing their role sincerely, you may be hurt to catch him or her lying, although you won’t be hurt too much, still.
All in all, a Neptune in 5th House synastry partner can mess up the dynamics of your life scenario, but not too drastically; and it’s almost certain that he or she won’t break it: rather, they will add some confusion and running around. They, on the other hand, can suffer much greater damage if they accept the submissive role in the relationship, even though you are unlikely to take them seriously in that role either.
In a harmonic scenario, Neptune in 5th House synastry partners can attend symphonic concerts and religious messes; but the true depth will not be reached until Neptune, the Fifth House, and the relationship as a whole are developed.
from A. Podvodny