Need Advice: Caught BF texting ex

Just found out my boyfriend was talking to his ex even though he made me feel like I was overthinking everything instead of trusting my instincts. Checked his phone and they’ve been talking again for at least a month right around the time I moved into my own apartment( we don’t stay together) I started avoiding his calls and messages the minute he left from visiting the night before but it’s only been a day and a half & I don’t know what to do from now. Should I reach out a confront him immediately or wait for a another day or two and then call him out? It’s the 2nd day and he hasn’t reached out let all compared to yesterday when he left that morning. I’m so confused.