I think my bf is cheating on me

I am 15 and my bf is 17 and we text each other but last week I messaged him and he never messaged me until Friday and a couple of days ago I messaged him and he never messages me back at all idk what to do he works at 6 am and gets off  at 9am to go to school but lunch I will message him and after school as well but he never answers me and idk what to think can some one give me some advice please?