Hi Pickles
Just letting you know you are not alone!
I'm also 28 weeks, my ex ditched me immediately after I told him I was pregnant back in Feb (despite us having lived together for 1.5 years, being in a relationship for 2 years and knowing eachother for 4.5 years). Apparently the 'timing' was all wrong for him and it wasn't going to fit in with his lifestyle - he'd gone back to college having lost his job and seemed to think it is impossible to combine a BA with a baby. Er, I went to uni with plenty of parents (some on their own who somehow managed to juggle the two!) Anyway, I digress...
Like a bloody fool, I allowed him to continue living with me as he had no other options, so had my head wrecked for 6 months: him going out at weekends, sleeping in the bed next to me with his back to me, not offering me any comfort when I was tearful or stressed and generally being an arsehole. He moved out 3 weeks ago, and apart from a couple of wobbles, i've enjoyed the peace. He is still in regular contact, wants to come to anti natal visits etc, just doesn't want me any more, isn't ready to 'settle down' - he's 42 btw. 
And I still love him < deluded idiot >
He has now become interested in the baby - wants to be a dad. But just not be with me. He seems to believe that he can return to college in Sept (when I'm due to give birth) do an hour or so a week playing 'daddy'. Then return to his studies and his selfish, single life.
I understand how you feel - the double rejection of not just yourself but the baby is just so painful.
I don't know what is worse - having them sod off altogether and not be bothered at all, or have them still in your life because of the baby when under normal circumstances if a relationship was over, you would not see eachother and therefore get over them.
Pickles, my GP has been wonderful - I am seeing a family therapist tonight, and she has referred me to a psychiatrist attached to the maternity hospital as additional support.
Grab any supports you can. As other posters have rightly said, concentrate on your baby - not his/her shit of a father! Try to enjoy what's left of your pregnancy and please message me if you want to.
Sorry if i've hijacked your thread a bit btw!