The short scene in which Pericles plays an instrument advances the plot in no way and is a mere fifteen lines long. The scene moreover, seems to be adapted from another text written by George Wilkins (who is considered by many to be Shakespeare's co-author in this play, and the primary author of the first nine scenes). The scene does not appear in the First Quarto or other editions, but some editors choose to include it. See Context for more discussion of the authorship of this play.
Simonides certainly arranges the marriage in a curious way. Pretending to call Pericles a traitor and threatening to banish him makes Pericles anxious to preserve his honor, while Thaisa declares openly that she loves Pericles. But Pericles says nothing about how he feels about Thaisa, beyond the king's initial questions about how he likes her, to which he responds tepidly. In the end, Pericles seems content to have married Thaisa, but not as enthused as is Thaisa, or even Simonides. Presumably Simonides's little game was intended to draw out the real feelings of the couple, which for Pericles seem mostly to revolve around honor, rather than declarations of love.