I have noticed, that sometimes I close one of my eyes when reading an sms when I am without my glasses. I this a bad habbit? I wear glasses constantly

Eye closure. Eye closure while reading does not damage your eyes in any way. If it helps you to read, feel free to do it.
Maybe. This is probably because one of your eyes is "stronger" than the other. If you don't do this too much, it is probably not a big deal, but make sure you have a recent eye exam to check if there is anything wrong with your other eye.