If you rented an apartment for yourself and you can "truly" afford it on your own then all this seems some what suspect. Outside of carpet stains, you mentioned no other damage by your roommate. So I see no reason for you to play hard ball. To be honest your posts come off like your mad he is moving out and now you have to pay the rent by yourself. All this ain't just over some carpet stains, which can be cleaned. So..................................
If you never had a roommate you'd still be paying to have the carpet cleaned because you got stains on it too. I find it hard to believe you'd jeopardize a long standing friendship over half a carpet-cleaning bill that you'd have to pay anyhow.
You demanding that he pay his share of the cleaning, while technically correct, seems petty and from the info you have posted makes you appear to be mad he's leaving you rather than actually worried about the apartment.
If there is more to it than that you have not adequately communicated it here.
I don't know how you arrive at the conclusion that I'm mad at him for leaving. If you were in my shoes, when the landlord does his inspection at the end of the lease in March, he will come up with damages that I am on the hook for. Roommate will be long and gone and I'm stuck with the bill. If I am angry, it is because I am the one in a precarious position. Why should I put my dick out there like that? Its not petty, its asking for some responsibility. Otherwise, for no other reason. A good suggestion was made regarding asking for a walk-through now, email was sent to the landlord earlier today asking for that.
Id be satisfied if the landlord has no issues, then I have no problem letting roommate go. Then at the end of my lease, another walkthrough. Any further damages are my responsibility solely. Pretty cut and dry. I dont want to play hardball especially with a friend, but its just planning on my part just in case it goes there. Some people would object leaving their name on the lease, or leaving a security deposit until March, jointly cleaning the place etc... I have no idea how the guy will act until he comes home this weekend and it never hurts to have a backup plan.