Oh, this is very complicated theme! TFs have different attitude to the gender differences. They haven't traditional family institute and females, if they exist significantly, have the same social role and thus the same psychology. I even can't say, that Bumblebee is a male in human sense. Autobots' psychology is really different, they are far more intuition- and feeling-driven, than human males. So, they meld both types of psychology, male and female. For Bumblebee Charlie is human firstly, her gender is not so important. Remember, what Steinfeld said "He is the same gentle iron giant as with Sam". But for Charlie, of course, he is male and the place for the beloved man in her heart was obviously free at the moment, when they met. So, from her point of view there can be some sexual subtext. But still it is very unusual and very interesting type of relations! It is close to the love in the Bible sense - compassion, mutual understanding, absolute trust and devotion, deprived of any biological ties and thus any commonness.