What you are feeling is totally normal, and as PPs have said, we've all pretty much gone through it. I had a hard time seeing really pregnant people for a while (particularly at the beginning), and it was a test for me when a good friend from college had her baby shower this past June (when Adalyn was 4.5 months old). I wasn't sure how I was going to do, but it actually wasn't as bad as I thought it would be.
You are definitely justified in mourning the loss of enjoying a full-term pregnancy. I never even got to make it to the 3rd trimester. I didn't really have a shower, never had those "oh my god, I'm so huge!" moments, and didn't really get to feel her kick much (also anterior placenta). DH only got to feel her once, about 3 days before she was born, while I was in the hospital. However, I couldn't ruminate in those feelings since it wasn't doing anyone any good. I acknowledged them, processed them, and moved on. It sounds simple when I write it, but I know that it isn't. Try to find someone to help you through those feelings--a counselor, a pastor, another preemie mom who gets it.
Anyways, I actually had a great experience with my BMB. I posted on there about her birth and updates and I had an outpouring of support. They ladies on there were some of my daughter's biggest cheerleaders, and they really helped us get through it. So, even though I have a Feb baby, I'm still an active member of the May 2012 board. They've said that even though Adalyn is technically a Feb baby, she's actually the first May 2012 baby! However, not all boards are like mine, so don't feel discouraged.