Can anybody with good relationship advice help me?

Bri • Hello everyone I`m Bri and I`m 24 years old and I am TTC 😃
Me and my boyfriend continue to get into it. I love him but lately Everytime we argue I love him a little less. The other day he was on Instagram dm with some girl and I'm like who's  that what y'all talking about and he deletes the thread and tell me I'm tripping! How? I feel like if you have to delete something then y'all probably was talking about something inappropriate to share with me. And he's like this my phone I pay the bill and I'm just like the argument wouldn't have went that far if he would have just communicated with me who she was and what they were talking about especially since I have the hardest time to get him to talk to me, I just don't understand, he has cheated in the past and I forgave him and we are moving forward but I just thought that was sneaky if the shoe was on the other foot he would have thought that I was cheating and there would have been nothing I could say. He doesn't see his wrong in what he did and is very unapologetic. He knows I like him hears but he always threaten to leave what should I do?