he liked my bff and now me ?

So there is this guy-colleague of my best friend in university, they are in the same group, who used to like her a lot for half an year- sending flowers to her, always asking her out, eventually they became good friends but he still hoped for smth more to happen between them even though she always saw him as just a friend and never wanted anything more. A month ago he added me on facebook and started texting me( i'm in the same course in uni but just in a different group- we are like 400 people in the faculty so we never met each other) and said that when he added me he didn't know who i was: even though my friend was mentioning me to him, we have a lot of photos together etc. eventually for the past month we started going out in the same group- with my bestie ofc, and he started texting me a lot, everyday asks me how i'm doing, always keeps talking etc, we run into each other a lot because it turned out also our jobs are near to one another, etc. now it's our exam session so you know- this is always a safe topic for conversation starter exams, school, work etc. and he never flirts in annoying way, in fact we have inteligent conversations which i enjoy and i'm almost certain that as soon as the exams are over and we have free time he will ask me to go out: just the 2 of us. i start to like him but the thing that bothers me is that i feel like i'm just the replacement of my best friend and even though she encourages me to try with him, she never liked him, has another boyfriend now etc, i have the fear that deep inside he is still not over her :-\ and another thing- he is not my usual type when it comes to looks, he has a charm, doesn't look bad and dresses good, but i don't feel like burning desire so what do you think i should do?