Fiancé thinks I like his brother!

Long story short, we went out and his brother was there, we were all hanging out talking then my fiance just walked away leaving me there with my friend and his brother (no big deal) then he says its time to go, we have work in the morning. As soon as we get in the car he starts accusing me of staring at his brother all night, liking his brother ect. He was drinking, I was not. And if I was looking at his brother it was out of respect because he was talking. I love my fiancé and if I liked his brother, I wouldn't be with my man! Why would I have a child with someone if I'm just going to go hang out with his brother. Ridiculous question I know. I'm stressing over it. I feel like I cant talk to him, he just gets so mad about it. He doesn't understand I love HIM I'm crazy for him! If he's going to be like this our whole life, I cant have a family with someone like that, Any help?:( what do you all think?! He just turned 30& I'm 25. Aren't we too old for this junk? Ugh. I feel like a high schooler again!