How to act during a breakup? BF coming over in less than 3 hours!! Help!

Okay let me be clear first of all I am not 100% sure this will be a breakup, but my impression is it will be leaning that way so I want to be prepared!!

Details: We've been dating for 5 months, we are super compatible for each other (and have readily told each other many times). Things were different at the beginning, they are not bad now, but there was more of a feeling of security earlier in the relationship. (By security I mean I felt like our feelings towards each other were more readily apparent).

One of the characteristics of our relationship is when either of us have a problem with the other one, we feel comfortable talking about it and then taking appropriate steps to fix mistakes or problems. No yelling, no emotional outbursts, everything is very rational and calm.

He told me many times if he had a problem he would tell me and I shouldn't assume there is a problem because if there was one he would be upfront. So as things didn't seem quite as secure as they were before, I felt a little more insecure and so tried to fix myself.

So this Monday after I had 2 midterms, we had a discussion out of the blue about how he isn't sure he loves me and he was thinking about this for a while. I brought up some things I noticed about his personality, he said he wanted to love me, he thinks he loves me, but just wanted to contemplate it for a couple of days to be sure. This sounds fairly promising right?

We've had very little contact since then (not normal for us)... I am not sure exactly how he is feeling but I do get the impression he has been trying to avoid me. The exact reasons why I think he will end things today I can't describe in words, you will just have to trust I have reasonable cause to think this!

I would have had no cause to think things were as serious as this. We have fun together, we share interests, we enjoy each others company so this is sudden. I do love him and think we are totally great for each other but I realize if he doesn't feel the same way there is nothing I can do.

I have been upset the past couple of days, haven't eaten, barely slept but I don't want to act weak today when he comes over. Please help!

EDIT::: Haha sorry this is so jumbled, it is really hard to keep my thoughts together on no food or sleep! I think the TL;DR sums it up if you are confused. Thanks!

TL;DR: BF coming to see me in less than three hours to possibly break up with me. I have been distraught the past couple of days by this and I'm tired of letting myself be victimized! How is the best way to act?

UPDATE:

So my worst fears were confirmed and he broke up with me. I didn't handle my feelings as well as I would have hoped, I did cry a little and said a few angry things at first. We ended up having a calmer conversation and basically he didn't feel happy anymore. He acknowledged I was a really good gf and thinks he might be making a huge mistake. I explained to him my feelings...and yeah... he ended up crying a little bit too. I guess my next post should be about how to deal with a breakup because I just feel hollow and absolutely empty. We've only been dating for about 5 months but I really thought he was the one... I really did... :'( This is hurting way more than I would have expected. Never has a breakup caused me to think I lost so much.....