Boston-born actor Ben Foster is getting hitched. No, not to actress Robin Wright, to whom he was briefly engaged in 2014. The actor best known for his roles in the western “3:10 to Yuma” and on Broadway in “Orphans” is engaged to “That ’70s Show” actress Laura Prepon. The couple attended the New York premiere of “The Girl on the Train” this week, and Prepon was wearing an impressive bauble on her ring finger. Prepon, who currently appears on “Orange Is the New Black,” is an outspoken Scientologist, but it’s unclear if Foster is involved in the controversial faith.