Did you mean october 2007? You've been together about 6 months?
Does he do anything to make you think he's cheating?
how old are the two of you?
What does he do when he feels bad? does he change?
Communication is probably the most important aspect of a relationship. You should be able to talk about things without feeling that you are 'nagging', and if he makes you feel like you are nagging when you want to talk, that is wrong. There's nothing wrong with someone wanting to spend time alone away from their partner. It's in fact, very healthy to have things that you do on your own, or with friends, without your partner. Taking/teaching a class, going out to dance, getting a hobby, are all things you can do on your own to help yourself grow and to have interesting things to talk about when you are together.
As for the sex, again you have to talk and tell him how you feel....not in a nagging way, or telling him that he's not doing something right, but when he does something you enjoy, you can tell him, "I like that a lot" or "wow, you really made me feel good when you did that". Men respond positively to praise. It's not uncommon for the sex to slow down after you've been with someone for a while, 2/3 times a week is still good, some people complain that it's 2/3 times a month!
So, communicate....be a little more affectionate, set up time that is just for you and him, do touching exercises, like massages with oils, hand massages, feet massages, etc. Plan to do little things for each other, and again, talk and communicate.
I welcome your thoughts, let me know if you want to talk more