Bf cheating with ex

So I started dating this guy about a year ago , he left his gf /BM of 2 years for me .shes been real petty about certain things since . He moved closer to her after she had the baby (back with his parents) , and then I found out I was pregnant but he didn’t want to move away from his daughter to live with me and I understood. But after she had her she was going over to his house spending the night and his parent love her but hate me so i kinda knew that was going to happen .

She messaged me saying that they have had sex and sent me text messages between them two , he denied it and said that they were messages from when they were dating .

I’m just very skeptical bc he has told me he’s always going to love her i but don’t want to know anything either bc I’m about to have his baby .but idk if she’s just saying this to get back at me .

Who should I trust at this point