You actually sound very childish and not equipped to handle any other individuals that may be in your boyfriend's life. And please understand, I'm am not saying this to be rude; this is what I perceive from some of the rather colorful language you use (cockblock,etc). It is probably for all parties involved that you leave now before you make everyone miserable.
One thing I have learned is that you will never be able to turn your boyfriend against his son OR mother, which it is clear that is what you want to do.
The way your boyfriend treats you and your daughter is the same way he treats his mother and his son. He's a really nice guy, who treats those he cares about with love and respect.
And it's unlikely that you trying to turn him against his mother and son will work in your favor.
I would expect, in a sibling setting, that a 12 year old would react to a 5 year old sticking her tongue out at him. It's not like she's 8 months old - she's goading him and he's reacting.
Yes, he's jealous. His mother has abandoned him and now his remaining parent is being taken away by a new girlfriend and her daughter who taunts him and you don't seem to see anything wrong with that.
I think best to leave him and let him get on with his life - there must be a woman out there who will love his son and appreciate how kind he is.
I agree with the others that it sounds like time for you to leave, since you can't drum up one iota of sympathy for the immediate relatives your boyfriend loves and is responsible for. As RockRose says, he sounds like a nice man who treats people very well. You obviously like him for that. In that, you want the others to dry up and blow away so you can have his niceness all to yourself and for your daughter's benefit. But when it comes to him acting with the same love and care to his own mother (no matter how much she grosses you out) and son, you clearly find it irritating that he would do that and criticize the way he does it and criticize them also. It just doesn't sound like your attitude is going to go away. This is a fight you should not pick and shouldn't try to win, but since you can't forget it either, you should try to find someone without this emotional load.
Especially regarding the boy, it might possibly help for you to remember that every child has the right to come first with his parent, just the way your daughter can claim this from you. I'm sorry this is not true in your own family, if you don't get along with them, shame on your parents. But I think you will always resent this kid's neediness and his life will be miserable with a stepmom who doesn't care what he is going through. He has the right to be #1 with his dad in every way -- emotional, biological, and legal -- and simply out of fairness, he should be able to act like a kid if he wants. Having parents who are unreliable (or one who is) is terribly tough on a kid, as you must know if you have a bad relationship with your family. When a child is faced with someone taking away the one scarce resource that props him up and makes him feel loved and safe (which is, especially at age 12, his dad's time and attention), of course he is not going to react like Saint Francis.
I'd stop throwing the kids together and stop going over to the family house, and stop snuggling with the dad in front of the kid, frankly if I continued to see him at all, it would be just the two of you at dinner at a restaurant every now and then. This man has given a kidney to his mother and you don't see him as having a value above rubies, you simply resent her. I'd say it's time to walk away.
Get the **** out of there. Sounds like nothing but trouble.
Your a young girl. Don't put up with kids **** lol sorry I known how u feel. Your in your prime years t settle. U I know your situation because I've been n your shoes, if I were u just break it off your young u settle for this. I dated a guy with his two kids we never had time together. His kids cursed and would act like animals we never had for us. I don't think u should b with him cuz u I need to accept his baggage to and if can't then just leave the relationship...im 34 and been thru this ur to going to be dealing with this.
If you haven't left him already, you need to sit down (just the 2 of you) and have a calm conversation about your feelings, and how you see the situation impacting your relationship. I can't relate on the child level, personally. However, I suggest planning dates that are just you and your boyfriend so that his son doesn't have the opportunity to feel jealous of a situation. That being said, if he plans time for just the 2 of you, he also needs to plan time for just him and his son. His child does deserve quality time with him, and having that may help him act out less when you and your child are around. His father also needs to explain to him the appropriate way to act towards a 5 year old. 12 year old boys are selfish in general, so him not wanting to share isn't uncommon.
Now, what I can relate to is the situation with his mother. My husband's father is a MAJOR thorn in our marriage. My father in law utterly despises anyone who does not sing his praises around the clock. Granted, I am NEVER mean to him, and will help him if he asks, I have no respect for him. He lies about EVERYTHING. No exaggeration. When he is confronted in his lies, he cries like a baby and blames his lying on other people. He depends on my husband for even the things he is physically capable of doing on his own. To top it off, he is diabetic and refuses to change any of his eating habits. He's already had things amputated. I've tried cooking healthy meals for him, meals my husband finds delicious, but my father in law will always find fault with them. Either it's: too cold, too hot, tastes burnt, not enough salt and pepper.... literally anything to criticize what I give him. Unless it comes out of a pizza box, it's crap to him. Keeping in mind that my husband and I do everything for him (literally the only thing we don't do is wipe his butt), there are still rumors going around town about us (me in particular) about how we are so cruel to him, And how we leave him to starve in dirty clothes. I work in the medical field, and his rumors have actually stopped me from getting a job I desperately needed, because they thought I wouldn't treat the patients well.
I finally told my husband I was tired of it and would be leaving him until he found a better solution for caring for his father. His father puts a ton of stress on our marriage, and we fight because of it. He confronted his father after I told him, and told him that his behavior was unacceptable. But it never should have gotten to that point. I felt like a horrible human being hearing him go off on his father. He said he wasn't willing to lose me over his dad, and things did get better for a while, but it's honestly just a repeating cycle these days.
In all honesty, I wouldn't have continued my relationship with my husband had I known the kind of troubles his father would cause for us. I love my husband more than anyone I've ever known, and I just cannot see life without him, so me saying that means a lot.
The above comments may be right about you needing to leave, but not because of you.