Does he like her or am I just trippin?

I have a thing for this guy and we are really good friends. In the beginning he would text me all the time every day and we'd hang out and got really close. Even had sex. It was all fun and kind of like we were in a relationship. Now it has faded Because sometimes I get jealous or he gets jealous and we fought a bunch for a couple of months.

But now he seems to be texting another girl more then me. she's actually in our friend group now but she flirts with everyone pretty much. She was interested in my guys best friend for a while there and they were hooking but that ended. she's already said she's not interested in him like that and he has told me before too. Even all of our friends tell me no they aren't interested in each other. But I still get a feeling that maybe they are Because they flirt when we all hang out.

He flirts less with me now...and texts less since we had fights. And I've noticed when he talks to her its fun and he likes to vs. he's boring talking to me. We still have sex sometimes and its fun like we are still close. But its still different between us. I'm wondering if he does like her. Once when he was drunk I asked him if he did and he said "what are you talking about" and then said "i donno I donno why do you care". And once he was super drunk and was showing me his texts and I guess he sent her a I miss you text and sometimes he thinks about making out with her. She didn't say much. My friend and his best friend tell me to not worry about it and that's just how he gets when he is super drunk like that and he won't do anything with her.

But still, I just am wondering if he does like her more then me or if he likes her as a friend but is losing interest in me lately. I probably sound like a stupid jealous girl...gah.