I think my husband is cheating on me with my sister

Hey guys, as the title states, I have a hunch that my husband of 5 years and sister are having an affair.

The first time I felt it was last year during xmas, when we were exchanging gifts my sister looked extra happy/excited to give her gift to him, to my surprise it was a freaking Macbook Pro and I was like… that’s a couple a thousand bucks. Later that night I was putting away dishes and I heard them murmuring in the kitchen, when I entered they hushed right away and looked flustered and started doing random stuff like putting away dirty dishes. Nothing really happened after this UNTIL yesterday so I just shrugged that whole thing off.

Yesterday I was waiting for my husband in the car at Walmart because we really needed a new car seat for our daughter. As he left he made a phone call and it was for a moment, still connected to the bluetooth. The name that popped up on the screen was “Steve” but I recognized the phone number. My heart dropped because that was my sisters number. When he got back I was like who were you talking on the phone with? And he said it was his boss, but his boss’ name is Devon.

I feel like I’m numb right now, I don’t wanna make assumptions but I don’t really know what to make of this?? I’ve just been doing errands all of today, I feel like I’m on autopilot/numb. How do I confront him? How can I confirm if I’m just not overthinking?

I watch a looooot of true crime about husbands killing their wives for life insurance, and now I’m overthinking the fact that we just increased my life insurance policy literally a few months ago, my husband was pushing me to do it because apparently I make more money now and we need to make sure our daughter is taken care of if anything happens. I’m also overthinking the fact that I’m always feeling drowsy really often.

Will really appreciate some input (am I overthinking?)

UPDATE 09/07

A little too soon for an update, but I’m so overwhelmed by the genuine advice and support from all of you. I’ve probably cried for about half the day today, my husband will be home shortly and to be honest I don’t know how I’m going to explain my puffy eyes away. I’ve done lots of research today, but I need to digest everything and plan my move carefully. I’ve pretty much settled on the assumption that they are indeed cheating because I’ve accessed the phone records and to me, it told me all I needed to know. I’ll try to update you guys when I can, but again thank you so much for all the advice and support, please know that I am not taking any of your suggestions lightly.