Harsh words make for an angry Mandy

I'm not normally one to get angry. I try to see the good in situations, and take things for what they really are. Overreacting is not something I think is necessary. Now, I'll preface this with the comment where from the outside, not knowing my circumstances, someone else may not know what is going on, and may be offended by my lack of communication. That being said...

I went to a company Christmas party with the guy I had been seeing-his company Christmas party. I was already starting to feel like things weren't going anywhere, but I didn't feel like I could back out on him. I go, open bar, other coworkers encouraging me, I end up shitfaced. A little embarassed about that, but whatever. The following couple days of work I have finals and the next week I have a huge presentation to give for work-gov't guys want to know about my thesis, so I was freakin' out a bit. I didn't have a lot of time to be visiting with people while I was at work, and I was working full days. I was tired and cranky. Saturday the 10th, I come down with the flu. And I mean "knock you on your butt for 6 days" kind of flu. The only people whose phone calls I was returning were my mom's and my roommate's...and that was just so they'd stop bugging me. Well, the day I got sick he called me to ask me to go to a movie-after I had already seen it with my college roommate earlier in the day-I didn't realize how bad my flu was until I was out and I hate cancelling plans with people. Well, I didn't call him back. Then I didn't work Monday, I worked on Tuesday trying to do the presentation and get a test running, but as soon as I did some stuff I went home and slept for 4-5 hours. Got up and tried to work on Wednesday, but my advisor sent me home 1/2 an hour after I got there-he said we would move my presentation (now its set for the 5th of January). Went back to bed all day. Didn't bother going to work on Thursday. Went to work on Friday, but was busy with work all day. Spent my weekend doing the Christmas shopping I hadn't had a chance to do while I was sick and catching up on everything else I put off. As of today (Monday the 19th) I still haven't spoken to him. This was not a direct attempt at being a bitch, it was more having other pressing things to worry about and not wanting to to dump someone over the phone while I was sick. But I can see someone thinking that I was blowing him off. I do NOT, however, believe that I earned the note I found in my drawer in the metlab this afternoon (as written-typos are not mine):

So, why did you use me?
So was that your plan all along? I didn't think you were that kind of person. I guess I wrong, I guess what amazes me the most is that despite how everyone says your so business like and formal, you didn't even have enough couth and respect to just tell me that you didn't want to date anymore. I would have respected that. The way you're doing it now is so childish, by avoiding and running away from the issue. If you think that I was moving too slow, I was! I was waiting for the Christmas party, you know the right moment, you of course you ruined that. I'm not the kind of guy that would make a move on a drunk girl, but I think you knew that too and that's why you did what you did. All this makes little difference now, I was just curious I suppose. Well I guess your off to use someone else good luck with that!

Now, I can understand him being a little put out. But really, telling me I'm a bitch in a note in my drawer? At least call me and leave a voicemail on my phone or something. I also kind of resent him saying that I would get drunk to avoid him making a move on me when I avoided drinking alcohol during any of our other dates so that he wouldn't have to worry about me being drunk. But anyway...

I'm looking for suggestions. What is the best way to respond to this? Do I write him a letter back responding point by point to his letter as to why things are the way they are? Do I call him? Do I confront him at work in front of our co-workers? I was basically trying to avoid doing any of the above, trying to wait until we could sit down and talk about it, but now I don't see that happening. Or do I just ignore it? Because now a bit of the bitch is welling up in me saying that if he thinks I'm such a bitch, I shouldn't even honor it with a response.

P.S. I wish he would tell me who this other guy that I'm using is...