Josh Hamilton -- Wife Blindsided By Divorce ... I Never Cheated On Him'

Josh Hamilton's wife Katie says she was completely "blindsided" by her husband's decision to file for divorce -- telling TMZ Sports she'll always love the baseball star.

Hamilton filed the divorce docs back in February ... seeking to end their 11-year marriage.

"It came out of nowhere," Katie says ... "There was no big fight or blow up. Nothing sparked it."

As for reports that Katie cheated on Josh, Katie says they're ENTIRELY FALSE ... "I never cheated on my husband. Are you kidding me? I did my marriage the entire right way."

Despite the shocking split, Katie says she has nothing but love for Josh -- and wants nothing more than for him to be happy and successful in life.

"I've always stood by him and I'll always stand by him. I support and love him now and down the road."

Katie and Josh have 4 young children together.

Just one month before Josh filed the divorce docs, the couple seemed as into each other as ever ... and went to a romantic dinner at Mastros. She posted a pic to Instagram and wrote, "Date night with my love."