Warning: Period of low self esteem

I think I'm a horrible person. At this stage in my life, I can't think of anyone whom I haven't upset.
I couldn't get along with 3 out of my 4 flat mates while I was in Invercargill. These people were my classmates, people whom at the beginning of our stay there, I had hoped we would get closer and have more understanding of each other by the end of our stay. Unfortunately, I managed to mess things up...

I can't get along that well with my brother. I tell myself things are different, that here, I'm more like an authority figure than a sibling, but still...sometimes the way he talks to me..there's so much contempt.

I could never get along with new groups of people I'm introduced to. I remember when I first came over to NZ, G introduced me to G's group of friends. In my effort to get along with them, I acted quite...stupidly. It happened again today actually, after AL introduced me to her group of friends. One of them reminded me of me...a couple of years ago when I was extremely sarcastic...and I did it...the sarcastic demon within me emerged...I hadn't thought that these people I was introduced to haven't known me for that long...I wonder if I've left a good impression. I think this is why..in some ways..I 'fear' getting new friends. I have enough trouble keeping my old ones happy and 'un'annoyed, how can I cope with new ones? Then there's the whole 'you just have to be yourself' dillema. IF I truly was myself, and didn't excercise self constraint on things I say...I tell you ...all hell will break loose. I only know 3 people with whom I didn't have to worry about controlling my yapping mouth. People with whom I could be totally myself...and not worry about what to say and what not to say. So does this mean I'm fake whilst Im amongst my other friends? In my attempt to exercise sensitivity, am I just stifling the 'inner' Kevin?