Inappropriate or over reacting

So my boyfriend and I recently got into a fight about another female. We will call her Ellie,

Now Ellie is one of those girls who crave attention from males, even tho she has a bf she goes looking for attention and affection from other guys, but she will act like this innocent little child when the males gfs are around. Now believe me when I tell you I’m not the jealous type. But she gets on my nerves

She’s not a good influence and constantly tries to get my bf to skip class (were in high school and this is my last year) when she’s upset so he can comfort her, he knows I hate when he skips class so barley does it unless we are in a fight.

Which happens often in which he likes fo fight about how we haven’t had sex, he is a virgin and younger then I am so I tell him he has to wait and not to rush things.

The other day he was hanging out with her, no biggie, they were gonna go see a horror movie. But one of those really scary movies that you see with a lover so y’all can snuggle and all that. I told him I wasn’t comfortable with the idea of it, since I knew how she was

He politely said okay with no argument, later in the night he was snap-chatting me and wasn’t in an environment that I knew, I had asked him where he was and said at Ellie’s house, I had asked what he was doing there, they were watching a horror movie on her lap top in her room

And then he just stopped texting me, the next morning he called me and asked me to pick him up, I did because I was worried about him. I had picked him up from her house, which made me mad

We started yelling at each other in the car, I was mad because he had slept as a girls house in her bed with her, home alone with her

Now I know for sure they did not have sex, I know him to well, but I thought it was inappropriate for him to be staying the night at a girls house

He said what was the difference with my friend let’s call him jay!

The difference between jay and Ellie is, jays mom had raised me since I was 2-18 my current age after my parents left, I was never adopted just looked after

I’ve always considered jay to be my best friend and my brother, we use to share a bed when we were younger so when I go over to his house I sometimes fall asleep in his bed or on the couch

Not some dude I had met 6 months ago!

He says I’m over reacting i say it was inappropriate and crossing a line. Who’s in the wrong here!?