Is it normal that i'm feeling this resentment?

My story is long and complicated but I am going to try to do the best I can. When I met my boyfriend he had a 2 and 1/2-year-old son who is now 3. His wife at the time was mentally and emotionally abusive, she was manipulative, narcissistic, materialistic, and just all around really horrible to him and honestly didn't give a shit about him or their marriage. When I came into the picture they were technically together but he wanted to end it as he was done being mistreated by her.

For the next few months life was shit for him, she would constantly berate him for everything he did, insult him, screamed in his face, she tried to lock him in a room and cried and guilt tripped him so he would feel pity and guilt over what he did, and tried to get him back and most of all she tried to take custody of their son. She gave him only a couple of nights out of the week to see his son for a couple of hours before he went to bed, no overnight, nothing. Then after my boyfriend started staying with his mom she finally gave in and gave him a couple of hours for a couple of days out of the week and allowed their son to go over to be with his dad instead of dad having to go over to the family house.

When I finally moved in with my boyfriend she flipped out and tried to take custody because I was now in the picture and she didn't like that. So after the two of them had a massage argument she set the custody to be he only got three days out of the week and only overnights during the weekend. When May came around she finally got off her high horse and allowed him to have a week on/week off schedule which was fine because my boyfriend was happy to now be able to see him every other week and his son was happy because he got to see his dad more. Everything was going well, and everyone was happy, except my boyfriend's ex-wife because she was in a vendetta that her ex-husband now loves someone else.

Now everything is starting to get bad and it's starting to get to the point where everyone is getting stressed out. For the past few weeks, SS has been complaining and throwing tantrums about coming to dad's house for dad's week. He apparently screams, cries, and throws a massive tantrum whenever he has to go. The previous week he complained to his mom and threw a tantrum about going and when HCBM asked him why he didn't want to go he said: "Oh SM yells at me." This pissed her off obviously and she asked dad as to why he would say this and if it was true. Of course, dad said it wasn't as he knows I don't yell at him, made me feel great to hear that he was lying and exaggerating about why he didn't want to go to dad's house. This caused me to realize that I am starting to resent him and that I am starting to not want to be here when he's here.

During this week's drop off SS apparently threw another tantrum about coming to dad's house right in front of him and wanted nothing more than to climb back into mom's car. He also had two crying fits when I finally got home after waiting 40 minutes for HCBM to leave. He is almost always in a pissy mood when he's here and dad has stated that it feels like he wants to be anywhere other than at dad's house and will usually hide away when dad comes to pick him up to take him home. It used to be enjoyable when he was here but recently he's been acting different. Anytime we take him to the park and I try to interact and play with him, he will push me away and say "No I want dad." He then will pout and run to hide when dad corrects him and says "No she can play too"

When we go out in public and dad has to do something quick like go into the bank, pay for gas, go into a store for something quick dad will tell him he has to stay in the car but SS will get fussy and throw a crying fit because he wants to go with dad, and anytime I tell him that he has to stay in his car seat that he's trying to unbuckle he will continue to throw a fit. I can never tell him anything for example; just the other day SS wanted a freezie before bed and I thought it was a bad idea cause he was already cranky and he was going to bed soon so I told my boyfriend "no don't give him a freezie, he doesn't need one before bed." Thought SS kept prying and dad caved in and gave him one. When my boyfriend did this SS came running and rubbed it in my face that dad said yes to it.

It irritates the shit out of me when he does this because it's like rubbing in my face that he gets what he wants because dad gave in and I'm wrong. I've had conversations with him about SS behavior but it goes in one ear and out the other. Recently HCBM has been spoiling her son and taking him to fairs, carnivals, events, and street markets, and getting him anything he really wants. She has been going out of town during her week with him and overall just spending a lot of money. Now since my boyfriend is the only one working right now we can't go and do the things SS wants and we know for a fact that he wants to go places and get things like shopping or Mc Donalds, or getting Slurpees etc anything that requires money he's up for and if we don't then he throws a fit.

When we are anywhere home or out in public and he gets mad, he will automatically make me a target of his anger. There have been countless times where he has screamed in my ear, tried to hit me, he's slammed doors in my face, tries to make it so I'm not touching his dad, and if I am he acts like I'm not allowed to and he's the only one allowed to hold his dad. There have been times he's tried to push me away and when he does this it makes me feel like garbage.

When he treats me like shit it makes me feel unwanted and this new behavior, makes me want to leave when he's with dad for the week. Then when he does his temper tantrum of not wanting to be here it's like my boyfriend goes MIA and I suddenly feel like I'm wanted by him either because he's just trying to win his son's attention and I'm left to go sit alone until such time when I'm wanted or when SS finally goes to bed. Though even then when he's being fussy then I lose more time. I'm really starting to resent and it's mentally draining to think I'm not wanted.

My boyfriend tells me that "Oh he's not doing it on purpose, it's a phase." but when does it get to the point where it's not a phase and ten years down the road he's still treating me the same? It doesn't make me feel any better when he tells me this, I mean I know some of it is normal toddler behavior but I would also like it if I didn't constantly feel unwanted in my home and want to be somewhere else for the week when he's treating me like shit and my boyfriend is MIA because he's trying to win his sons attention because he threw a fit about coming here.