Hi beautiful ladies, I just want a little advice on a situation in my relationship and I don’t have a woman role model to go to so yea (sorry it’s kinda long)

So I’ve been dating this Guy since November and we just recently found out that I am almost 3 months pregnant. We are both very happy about it. This would be my first and his second btw I’m 20 and he’s 25.

So recently I I have had reoccurring dreams about him cheating or having a female on the side. And I have casually asked him about it for two weeks now and he denies but I’m still having the same type of dreams. So this morning, although I’m typically against it, I decided to go through his phone and I discovered that he is talking to and has been talking to for a long time (before we even got together) some girl. He flirts with her,says he likes the way she looks, and dresses and puts heart eyes under her post, they also have had multiple conversations about how he tried to pursue her romantically and how she felt about him dating 2 different girls while they’ve known each other but they also have regular friend conversations. So I finally put 2+2 together and found out that the girl is actually his SILs little sister. So she will always be around and she’s not some random female that he met out and about on his own. Usually in a relationship I say if a person was in their life before me then I don’t necessarily have the say-so to tell them who can and can’t be in their life, but this is where I draw the line. I don’t know if they’ve had relations sexually but I don’t feel comfortable knowing that she’ll always be around and they are as close as they are. Sooo I’m not sure how to confront him bc I will have to start with “I went thru your phone...” smh this the first healthy relationship Ive been in since my abusive boyfriend and now this shit. HELP 🤦🏾‍♀️