Bf masturbating to porn?

Update/ he used to follow girls on Instagram(models and porn sites) and I talked to him about that because it bothered me more than the porn and he's not always been honest with me about everything and I do have minor trust issues. I explained that it was rude to me and that I felt disrespected because of it. I actually did tell him I didn't care about porn (because I didn't want him to freak out and though I knew it bothered me a lot it didn't nearly bother me as much as the whole Instagram thing) and I much rather preferred that if he had to do it to anything that wasn't me that it was porn and I know I set myself up for this but I'm pregnant too and honestly I get so emotional about it and if I try to talk to him and ask him to not watch porn I'm afraid he's going to get really angry and say that I said he could and honestly I just have no idea how to bring it up 

Thanks for all the replies. I know this is lengthy and I really just need to be upfront about it and not take no for an answer, I feel a lot better about bringing it up knowing I'm not the only one