The experimental work presented in this thesis studies and characterizes decoherence of excited matter-wave solitons, known as breathers, in neutral lithium-7 BECs. Motivated by the rich pool of theoretical predictions for beyond mean-field physics, and recent work in our lab which experimentally realized the production of breathers, we study the lifetime and decay of breathers in a one-dimensional (1D) wave guide. We report measurements of decoherence and dissociation of breathers in a quasi- 1D geometry, and attribute the dissociation features to three-body loss by comparing against numerical results from the 1D Gross-Pitaevskii (GP) simulations in the mean- field approximation. We find that in the low atomic density regime for breathers, breathers no longer dissociate and deviate from the GP simulation results. In this regime, the breather damps out and embodies signatures of relaxation associated with beyond mean-field number fluctuations.