I really really need help and a good answer for this question. Please help me.?

My bf met this 26 year old nursing student due to her assignment,she is from India, very attractive , My bf is 35 years old and i am 33. Well, they both exchanged number the day she interviewed him, and they started text messages and talking. I was very supportive of their friendship, very sweet girl. I don’t check his phone but yesterday i went in his messages and i saw she messages him all day long and he messages her back all day long too, He is telling her when he came to work, when he is going home, He messages her about every minute details. Worse of all after 18hrs long day,after he put his kids to sleep. He is staying up to text her and they are talking about what he like, what she like. She is taking so much interest in his kids. He fell asleep while texting and then in the morning he said sorry to her. Is it just a friendship? Or is he growing feelings for her? She show so much care for him, Did you eat lunch? Hows the kids? Did they eat good dinner? Everyday she asks about kids and what they going to do today. I don’t know if i should be supportive of this friendship anymore.They just met a little over a month ago. I didn’t think you can become this close just in a month?