I still can't control it
The word 'still' has connotations of remaining, long-lasting, and still going on. This could mean that their relationship has gone on for a long time and even though they should be used to each other by now, the feeling of not being able to 'control it' still applies and this means that every time they are with this person, they always think that they need to act a certain way around them, or be extra nice or whatever, in order to make their lover approve of them and continue liking them.