snooping threw my ex fb

I was going threw my bf Facebook  and I see a message from a women writing behalf of her friend saying do you still like Rachel and would u like to get closer to. He said yes to the questioned . Rachel has a fiancé   And because they was having problems she felt the need to get her friend write to him. In temper I called Rachel a slut. And he didn't agree and he don't see why he should stop talking to her. He wants to get back with me but I'm not to keen. He also don't reckon she's a slut and get pissed of when I say it.