2017 is my year on parenting plan to claim my kids. Can my boyfriend claim them and me if I didnt work much this year? He's married but separated.

I get to claim my kids on taxes every other year according to a parenting plan. This year I didn't work much. My boyfriend wants to claim me and my kids. He is not their father and he is married. Their father gets to claim them in even years. Can he claim me and my kids?