Complex sentence: Around this time, Walter dated his lab assistant, Gretchen; however, he abruptly left both Gretchen and Gray Matter Technologies, selling his financial interest in the company for $5,000.
Split into simpler sentences: Around this time, Walter dated his lab assistant, Gretchen. However, he abruptly left both Gretchen and Gray Matter Technologies, selling his financial interest in the company for $5,000.