Complex sentence: The two outlets then began to share ABC programming (which had previously been exclusive to WABI) through an arrangement that ended when WEMT (now WVII-TV) signed-on in 1965 and took the affiliation.
Split into simpler sentences: The two outlets then began to share ABC programming, which had previously been exclusive to WABI. This ended ended when WEMT (now WVII-TV) signed-on in 1965 and took the affiliation.