Partner cheating?

So I had a really bad feeling a few months ago my partner was up to something. I tried to shake the feeling but physically couldn’t. I was talking to my best friend and explained how I felt. She said I wouldn’t have been feeling how I was for no reason. A few days later a girls name popped up on my partners phone on snapchat and I was like that’s odd. I didn’t know he was friends with this girl. ( no issue with my partner having female friends) he was super sketchy about me seeing so I asked to see his phone and I saw he literally had a running streak with this girl and they had been chatting really late at night. Unable to see what was said due to it being photos. I explained to him how I felt and that i felt uneasy he was messaging this girl so much when he doesn’t hardly Snapchat me when we are not together. He said sorry and said they were just chatting about tattooes. I let it slide obviously still feeling a bit weird about it all. He said he wouldn’t message her again ( I never asked him to do this). I took his word for this. A few weeks later I catch him yet again being sketchy and snapchatting her a lot and I’ve just seen she’s broken up from her long term partner. I then ask him out right what the fucks going on with the constant chatting and he blerts out “ nothing happened” I didn’t even ask him anything within that context so now my minds racing and I don’t know if I’m over thinking or my gut is right? Ladies please help!