COVINA, May 17 (UPI) — Leaders of the American Baptist Churches of the Pacific Southwest have left the denomination, primarily over its handling of homosexuality.     The region's board of directors unanimously affirmed late last week an earlier recommendation to withdraw from its "Covenant of Relationships and Agreements" with the American Baptist Churches USA, Associated Baptist Press reported Wednesday.     The national denomination, which has its origins in a Civil War-era split from what is now the Southern Baptist Convention, is based in Valley Forge, Pa.     "God's heart is broken when sisters and brothers in Christ divide over matters...