Models for your compositions

It's important when composing (and especially when composing in a particular style, like your current Romantic style compositions) to work from models. They should be used throughout the composition process: at the beginning, for inspiration and overall structure; and as you work, for help in solving any problems you have. When you run into a problem, don't just resort to trial and error: go back and see how a composer solved the same problem.

For example, if you've got a violin melody that you like, but don't know how to develop it, look at how Dvorak did the same thing in his violin pieces; if you want to write a string quartet but are not sure what accompaniment patterns to use, look through the Schumann quartets for movements with the same tempo, and adapt a figuration; if your piece doesn't have enough harmonic direction, look at how Schubert kept harmonic direction going in his string quintet.

Here are some good Romantic models for you to use:

Piano:
Schumann Phantasiestuecke
Chopin Preludes
Schubert impromptus
Mendelssohn Songs Without Words

Violin and piano:
Dvorak's Romantic Pieces for Violin and Piano
Wieniawski Romances sans Paroles op. 9
For something a bit more complex
Brahms' Violin sonata op. 78

String Quartet:
Schumann Quartet no 1
Mendelssohn Quartet no 1
Mendelssohn Quartet no 2
Schubert "Death and the Maiden" Quartet

USE MODELS! Don't try to do it all yourself - you are doing it the hard way if you do.