Complex sentence: A trip to Paris gave him the opportunity to attend life-drawing classes and to paint, but it also left him with a large amount of debt, and so he returned reluctantly to the dull work of producing advertising art in Chicago.
Split into simpler sentences: A trip to Paris gave him the opportunity to paint and attend life-drawing classes. However, it also left him in debt, and so he reluctantly returned to the dull work of advertising art in Chicago.