Boyfriends ex has cancer

We had an agreement my boyfriend would not talk to his ex. Then one day she called him to tell him she has cancer (lymphoma) so hes like I'm going to be there for her if she wants to talk or if she needs a ride to the doctor or something.

I still can't stand it. They talk on a daily basis almost and I hate how he stayes up to date on everything. I get calling once in a while but I think its too much. I feel like he's trying to fill the man void in her life.

Am I being selfish. I dont know what to do I hate them being in each others life it's like they don't know how to not cross lines.