How do you tell if a guy likes someone as a friend or more

There's this guy that my friend and myself like.( Long story short, I've liked him since summer and made small talk with but my friend made him apart of our friend group then started to like him and is ten times closer to her then me) He told me he is to busy for a girlfriend but he only said that after my friend group was teasing him for not giving a girl his snap. And I Believe him he's a busy person but he flirts with my friend all the time and I just want to know if he's interested in her.

*** They don't know I like him... And it doesn't bother me I rather have them both as friends then mess it up

If you have any tips, any at all they will be helpful. Thanks