i can only give a brief guess, if you want a detailed one you are feel free to contact me personally (
[email protected]), telling me your family background
now considering your 'good' form teacher, the most reasonable reason that you have such effect is that you sub-consciously set her to be the model of a good partner as she protect you so much and give you the sense of safety so much. you even want your future spouse to be the kind of person like your form teacher. so every time you see her, you have the feeling of falling into love with.
as this occur, you start to question yourself about whether you are les or not. then you begin to generalize your feeling to other similar female teacher, hoping for another person like your form teacher.
if you really want me to analyze more in a rational way, or in an emotional way, please really feel free to contact me personally. by the way, i suggest not to be molded by the sayings of your friends, as this will sub-consciously affect you. wish you find your answer