It is not a easy decision. * ^) K, l' Q/ E/ O0 V& M6 l$ e0 `/ q
If I were you, I do not reject this offer for now, ask the possibility to do a part time supervisor.
first, congrats on the supervisor offer. second, you need to make your timeline more clear: are you planning to do BBA right after diploma (so in april)? or will you be doing BBA in september?