Are they sleeping together

So I found some messages in my husband phone to my sister! I want to know what you guys interpretation of this is? I'm hurt but it's been a week and I still haven't approached them yet.

At the same time I want to know more what was the conversation before this because this was all I could get a hold of. Because everything else was erased. Now I don't normally go through my husband phone but my intuition was so strong the first time I ignored it and went about my business but then he started acting insecure, questioning me about my whereabouts and arguing with me for no reason. then it happened again the phone was right there again, it went off and I decided then fuck it. He been acting weird I want to know why. And I then saw my sister's name and went strait to it. And of course I see these messages. Smh

The crazy thing is I don't really see her flirting but he sending you gifts in secret and your excepting them. Same thing he bought me. You sending inappropriate pictures (no nudity but the pictures weren't your everyday outside selfie ) and you haven't once came to me about none of this behavior.

I am going to confront them both

Some other stuff he bought her with our money smh.

I wanted to add that in the past my sister has done this to a close friend of hers long time ago. (Slept with her boyfriend while still being close friend with the girlfriend) I never would've thought she would make me her next go too.

Update:

So I went to the doctor to get tested because my bladder was hurting bad and I wanted to know why....came to find out the doctor said I had an STI called trichomoniasis. She explained to me how it travels and everything and told me to ask him and garenteed me he'd be in denial. He was, and actually tried to flip it on me.

Anyways along with these messages I found I went through his timeline on his map quest and saw that he's been going over her house after work and staying until 5 in the morning. I'm sleep at that time a night because I have to get up early for work 5am. He slowly crept in the house and thinking I wouldn't here him, took our daughter and played her in her room.(she slept with me) came back in took his clothes off and went to bed. I woke up got myself together and went to work.

Anyways I confronted him and he denied..and made up lies even with proof , he try to switch it up to where he's not doing nothing and if he did it's my fault. Smh ..but as far as her I can't get in touch with her. She has been avoiding me. I've tried for a couple weeks to give her a piece of my mind. But she refused to talk about it or even reply back to me in anyway.

You know this hurts because she's my sister and I never would have expected her to do this to me. But I'm going to stop trying to get answers and just eliminate them out of my life.