boyfriend trouble

Hey guys do any of you have a long term boyfriend or have had one in the past?

 My boyfriend is a really trustworthy guy and he's been cheated on before so he would never do it to someone and so for the past year and a half I've never once worried about him and girls talking. Like the most I've ever worried is to ask him about her and he'll re assure me and then that's it I move on..

 But there's this girl. And she's so not his type in anyway looks wise but she is pretty and she has an amazing personality just like his.. and well she joined his friend group and kinda lathed onto him more than the rest and they text daily and dm and Snapchat and they even like voice chat often too.

 He said I have nothing to worry about but it hurts so bad and the worst thing is that I'm not even mad I just love him so much the pain is like overpowering to the point where I can barely eat or sleep. I can't think of anything else because I'm constantly worrying they are talking right this moment..

 I know I can't help it and he knows I'm worried but he can't cut her out. How do I just learn to live with this? Has anyone had this situation before? Thanks:/