Complex sentence: This makes Johnny realize that it just won't work, that marrying Julia on these terms will be more of an encumbrance on his freedom than he can abide, and he leaves to meet the Potters to sail to Europe.
Split into simpler sentences: This makes Johnny realize that it just won't work, that marrying Julia on these terms will be more of an encumbrance on his freedom than he can abide. He leaves to meet the Potters to sail to Europe.