What do you guys think?

My boyfriend added this girl on snap and the girl added him back and he tried to hide it like when it came on his notifications and I told him what was that and he said, it’s nothing like at first and then I told him you added her and he’s like no I didn’t, she added me. And I’m just like bro stop fkn lying. There’s no need to lie? And he’s like okay I must’ve added her a while back but idk who she is. And I told him dude you look more stupid trying to lie than just saying the truth. I won’t even trip if you’d just say the truth. And he insists he doesn’t know her. I’m so fed up. Been dealing with his lies and him adding woman for years now....I got a baby with him and I work a little part time job while he works a full time job. I feel stuck