I've had my betta for 3 weeks now and when I put a mirror up to him to see if he will flare he doesn't. he just stares at it. and when i first brought him home and he saw my goldfish he flared up now when he see's them he doesn't care. Is it okay for him to not flare? or is it telling me he is sick?

Does your betta seem healthy except for not flaring? Does he eat and swim around OK?

Yep he swims around all day and when i come to look at him he'll swim around and is eating normally

I now have 12 bettas, 9 males and 3 females--they are all different in their flaring attitudes! One of the girls flared at the store--didn't like her female neighbor--so that's why I bought her. But she hasn't flared since. Some of the boys flared when they first saw one of my new bettas but now they don't care. A couple of them I have to keep their view blocked from the others or they keep flaring constantly and that's not good either. So your guy is probably fine.