My boyfriend and I have been dating for about 3 days now. When we got together he was all sweet etc.. And NOW, it's the third day and I get worried when other girls talk too him, or he talks to them. Whenever I get on Facebook I go too his profile and notice that he says Hi to A LOT of them on their wall, and it bothers me, and I'm afraid he's going to cheat on me. I don't want to say anything too him because I don't want too ruin us because I like/love him a lot, and I'm worried about what he says too them in chat or when he texts people.

Well if you have trust in him than you shouldn't have problems with him talking to others.

Seriously all one can do it trust, if you don't have that you might as well just give up now. You stated that you have only been going out as a couple for 3 days. I wouldn't worry, it's very healthy and normal to talk to people of the other gender. So unless he gives you a legitimate reason for worry like you saw him kissing someone else then just go on about your life and be happy.

Three days and you are already worried and watching him on Facebook. Sorry this has to be either a very young age dating, where you have not learned to trust the other person.
Or perhaps you have been hurt before and can not trust.

If you are ever going to have a good and real relationship you have to learn to trust and date properly

How old are you both, and how much time do you spend in person?

Is there a reason for you not to trust him? Are you normally insecure, or been cheated on before? Socializing is not cheating, If that's all it is, relax, and think before you act or speak, and be calm, cool, and collected, and under control when you do act, or speak, no matter what's going on, or how intense you may be feeling. At least then you won't scare the heck out of this guy you're dating, or make him think you are a moody, controlling psycho. That's no good after just 3 days of dating.