Who should I confront, my boyfriend or his ex

My boyfriend’s ex loves posting about him and how she feels about him till now and just very recently, she said something about him that sounds like it just happened recently. She shared how much she hates him and how he’s an asshole for jerking off on her after reconnecting and apologizing to her. She didn’t made it clear if she was referring to him but knowing that he was her only ex, i’m assuming it was. I just don’t know who to approach. If I approach my boyfriend, i’m not sure if I can trust what he’ll say.