Am I over reacting or is he cheating??

So we were having a family function with my cousins and parents and siblings and my bf gets a call and I’m like oh who is it and he’s like just a client I’ll call them later and then I’m like it’s ok to call them back now, and he’s like no and he walks outside and I’m like where r u going and he wouldn’t let me see who was calling, and so he runs down the street bc he doesn’t want me to see his phone, and all my family saw this, and my cousin confronted him and was like what’s this bullshit about and my bf said his ex was calling him and my bf told me he has never had a girlfriend before me so he’s lying, and then I asked why wouldn’t u just tell me and why is she calling u and he said she always calls me and I was like why don’t u block her number and he said he doesn’t know how which is bullshit cuz he’s a tech guy!!! And I was asking him about it and I asked how did he know it was her and he said he knows her number bc he always calls him and he never answers!! He said it’s an ex from a few years ago but he only just got a new number last week like WTFFF ugh this hurts but idk what to do