What to do..

So he was drinking not so long ago and left my house (we don't live together) like that. Tried to stop him from driving only to end up being left on the side of the road. Couple blocks down. We're having a baby soon. Anyway he had left his laptop etc and I saw an incoming ft call from some number. I call back private and it was a woman's voice. Anyway. I tried cutting him off and he came back apologizing etc for being a jerk that night. Go thru his phone today and see this person previously texted him these emojis: 😈🍑🍆 and "hey sexy." He replied on a different day with "yo." We were going thru movie list on Netflix and came across a movie he claims to have seen with me which I know damn well I didn't see. Anyway feel like he might have cheated with whoever this person is. He's the one who owes me respect not her but I do feel like anonymously getting info to further investigate since I have the number. No one wants to get played pregnant. I don't. I know what to do if I confirm. Sick of being loyal and lied to by men. Anyway how should I reach out to this person and what should I say without bluntly asking? Should I pretend to be him? See what I find out?