fed up

for the past 4 months i have dealt with bs from my fiance's family.. i am so sick of it already i just learned that in july of 2010 when i became pregnant with my son they didn't like the idea because my fiance already had a daughter 11 from a previous relationship. and his sister was upset about it but they were 2 faced cuz they never said anything about it at the time. his mother and sister is friendly with his ex and constantly talks about me and my son to her and i am really pissed about it.  my fiance and i moved in together in may 2 months after my son was born and they were pissed at me cuz he moved in with me.  his mom even went so far as to sell all his baby stuff that my fiance bought for him. his sister constantly tells me i better realize its not just about my son he also has his other daughter ...like i need to be reminded.. i knew he had a child and i accepted that but why are they being like that towards my son and me for. it hurts me that my son of only 6 months is being blamed for everything. these people need to grow up my fiance has stuck up for me but everything i have been dealing with is tearing me up inside i try to smile but i am hurting:( i feel like cuz of my babys daddy's family interfering like they are i feel like me and him aren't as close but i love him and i know he loves me but his family is really putting a strain on our relationship. they want to see my son but until they can stop with all their bull i have said no but i feel like the bad guy and i feel like i'm making my guy choose between his family and me i'm not but he takes my side and is pissed at his family for what they have done..i just don't know what to do anymore...