Am I jealous? or Justified?

I am currently engaged to a man whom had 2 children previously by two different woman. The oldest child we only see maybe 4x a year, due to his schedule and his mother. The other son who is 5 now, we see more than EVERY WEEKEND. I have a child from a previous relation & together we have another child. Here is where the trouble begins. His youngest son comes over every weekend, but doesn't acknowledge the things I do for him. His father hasn't worked since we had our child in Feb 2010. I work 40 hours a week, I supply clothes when needed, thou even when I buy them they end up at his mothers and she doesnt return them, even after I ask NUMEROUS times. She apologizes the day of and promises to bring them back, but I have YET to see any of them. I supply his Christmas at our house, yes for 4 children, on one (1) income, and its not the greatest income. My fiance drinks and smokes and I provide for that as well, when I am barely getting by with the bills. to assure that everyone is happy and provided for. I plan group vacations and the only thank you I get from his son, is FORCED, becuase his father forces him. He won't give me a hug, unless its forced. He is rude and when I tell him to do something he wont, or he will ask his father again. Its like I am fighting a losing battle. His father & I love each other and yes we fight & argue. I tend to zap out, when I have a bad day at work and I come home and the house is a mess or things are done like they are suppose to be done, but thats normal, right?! Don't get me wrong I love his son to death, but there are times when I think its his mother's doing. I have a feeling, and Im not the only one whom has noticed or assumed the same, that his son's mother wants my fiance back. His father and I will mention us getting married and me being his step mom and he will say well you aren't married yet so you aren't my step mom. Then, I will be flirting play fight with his father and straddle him on the couch and pin his hands up like we are play fighting and his son will jump right into the middle. I will tell him to back up, its just daddy and I play fighting right now; and not 2 mins later is he latched onto his fathers arm yes while I have his(fathers) hand saying I love you daddy. But yet 10 mins ago you guys were play fighting and you stopped b/c you were tired, once I start any initmate contact with his father, he gets right into the middle of it. Or recently we went on vacation and I paid for the entire trip, food, lodging, waterpark, arcade and extras, and he kept telling his father Thank you, thou his father would tell him I paid for everything, his son would say " well she doesnt pay for my moms house " Really?! So here is when I got to ask if I was out of line ... on our way back from vacation my fiance and I got into an arguement, becuase I was beginning to see that he is very disrespectful and unapprecitive too. So in the mist of us fighting his son is "LAUGHING" at me, as I tell his father to cut it out its not funny, you need to stop. His father is going on and on knowing its getting me and his son is just laughing. So eventually he pushs me to edge and tells me that he doesnt care, he could name 5 girls to replace me so I stopped my vehicle and told him to get the **** OUT OF MY CAR, call one of his BITCHES to come get him and don't worry your son can go with you. So he told me no, so I told him son to get out of my car since he wanted to be rude, he could go with his father, his father said NO again. So I hopped out of the car and proceeded to his sons door and opened it and went to reach for the buckle, when his father jumped out of the car and became physical. Needless to say he apologized later but said I was attacking his son to get at him. Though in a way he was right, I also did it b/c I was tired of being disrespected by a CHILD. whom I have NO BLOOD relation to, but treat like my own. So his father asked me if I was jealous ?! Is this what it is .. am I jealous of his son?! I'm not sure if its me with the issue or him and his son ... Mind you this is a man whom says he'd rather spend "our" wedding night with the kids, instead of us alone ... This is also the man whom sleeps on the couch when his son sleeps over, thou his son has a bed & I have seen him spoon with his son in a way that he use to spoon with me, but no longer does. I told him if he doesnt want to be with me, just let me go. But he says he loves me to death if he didnt he wouldnt be with me trying to work things out. I just don't know anymore ... is it me? or am I justfied in feeling the way that I feel ?!