Is it normal that my BF calls other girls kotek? I know that it means kitten.
To be honest Petrushka it isn't about what he calls the girls its about the trust between yourself and your boyfriend. If you trust each other and make sure you know the boundaries of your relationship then a few names or txt messages should mean nothing. If he tells you it is harmless and you trust him, then go with it. If you don't trust him then its time for action.
When i have been in relationships i have always said to my partner that i'm not really bothered what she says/txts etc to other male friends. As far as i'm concerned i will trust her and visa versa. For this trust to happen i also promised all my partners that if i found there to be something that crossed the line (they had been going behind my back) there would be no talks, not saying your sorry, that would be the end of it. As its Wimbledon at the moment i say to them 'the ball is in your court, if you are faithful, i'm cool, if your not, we are not cool'
I no this does not really give you an answer to your original question but i would concentrate more on the trust between the two of you than about a silly name that could be harmless sent over a txt msg.
I hope this helps, even in a small way
T