Is it me?

My bd & I have been together for 3 years.. We have a daughter together, I had 1 before the relationship tho (2 girls for me, 1 for him) but he claims her as his on too. Lately he’s been acting different & he says I’m acting insecure because I wanna look in his phone. He gets defensive saying “do you pay this bill?” 🙄 I say no & have an attitude until I go to sleep.. I’ve snuck through his phone but the convos never add up. I know he deletes everything & also he goes outside to have phone conversations now.. I no longer say anything, but my attitude instantly changes.. ALSO I FOUND LIPSTICK IN HIS CAR & my mom & sister said it isn’t theirs. He says it’s his sisters, sisters friend, or his cousin wife’s. Deep down I feel like there’s someone else though.. I’ve confronted him plenty of times, but maybe I should back off.. I know we need space & I don’t need to know everything , but it bothers me. I open up my whole life to this man & for him to do me wrong (if he is), is gonna piss me off. He doesn’t answer his phone around me, just watches it ring & we haven’t had sex in a while either.. I just don’t know.. I’m really just venting but I’d love to hear y’all opinions..