Idk what to do or believe ... what should I do ?

My son's father has been talking on the phone with a girl from his work. So he thinks it's fine for him to have friends of the opposite sex but I can't. When I had my co workers number it was a problem. And he said he didn't have any female numbers at all so I deleted the numbers I had. Come to find out he been talking on the phone with a girl from work he says he only friends with. How is it only friendship when he talks on the phone with her longer than me( I looked at the phone bill so I know how long they talk ). He calls her before work, when he gets off and even in the middle of the day. Like I don't understand and I'm on the verge of snapping out. I'm already depressed after giving birth to my child 7 weeks ago. I don't know what to do. He claiming they just friends but it seems like it's something more that that. He didn't even tell me about it. I had to find out. And I wasn't even trying to find out. I just so happen to see this number come up a lot on our phone bill.