UPDATE - My Dad moved in with his girlfriend... I am struggling.

Here is my original post just if you wanted further background. https://www.reddit.com/r/relationshi...rm_girlfriend/
TLDR - I have visited my Dad and his girlfriends new house, twice for a few days each time. I have felt very strange in the new situation and dynamics but they have all been very welcoming to me. Any advice on how to get pass these worries would be great. All points of views are welcome regardless of what role you play in your blended family experience (past, present or future.)
Hello everyone, I'm Mason and I am a 14 year old boy! I just wanted to update you all on the progression of my new situation since my original post. You were all so great with the advice that I really wanted to do this.
So I took the advice that one or two of you gave me and decided to ask my parents if I could split my days shorter when visiting for the first time just in case I found it overwhelming. They both agreed and didn't make me feel awkward about the suggestion at all. I have completed my first set of visits and went back a second time.
My Dad introduced me to my new bedroom which was a decent size. He gave me a budget and then took me out to get loads of bedroom related stuff. I really enjoyed it and it was nice to have some ownership over my new space. My Dads girlfriend cooked a pasta meal that I thoroughly enjoyed and we all had a movie night. My first night in my room felt a bit odd and I had a restless night but that soon improved. Me and her son got on well enough as usual and we had a laugh during the movie night.
By the second day it still felt strange. I wanted to go back home at it was so unusual to be in the house. The realisation hit me that this would now be a regular thing. They are both very loved up and affectionate I don't really understand that feeling of weirdness about it as he has moved out a while ago and I have seen them together many times. I guess I will work through it the best I can. My Dad and her son get on really well which gave me a pang of jealousy but I really tried not to show it as I believe I am the one with the issue and not them. My Dad had given me one on one time so there was no really reason to get envious.
Overall I am happy for them but I did genuinely try and any insecurities or worries I had, I put to one side and planned to wait and see how the second visit was... By the second visit I currently do feel a bit like a guest (a well treated guest) at a residence. They have a solid dynamic that I am trying to find my place in and all have in jokes that I don't really understand. I never noticed this before but I realised that they all get on extremely well and have obviously spent a lot of time together in the past. I am trying to fit into their routine and ways of doing things and I realised his girlfriends routine seems dominantly the way things are done in the house meaning she and her son get by more easily if that makes sense. I feel I need to be on my best behaviour at all times and am constantly not wanting to offend intentionally. I have a feeling my Dad stayed at their old place rather a lot and this is why they get on so well on a day to day basis. This made the green eyed monster come out. Pretty sure this is fairly normal but Dating.mobi helps me to chill out a bit as well as the suggested writing it down on paper. I have a lot to work through and I have decided to try and be more self reliant now that I am getting older (slightly sad but cool to.) I know they will listen to my concerns if I am worried. Another piece of good advice I got on here. I have no idea why I am not level headed on certain things anymore, the emotions just pour out via my mind and then settles down.
Any advice, suggestions or your own experience of this would be appreciated. Please give it to me straight, I don't need mollycoddling...


Source.