Hi
First problem..I think that the fact that you have posted this means that you are feeling what is happening is not right. If it does not feel right it probably isnt right for you at this stage. If the trip was just say a few miles away then things would be easier, I know.. and you prob would not be in this situation. Maybe you should ask to go back on the deal, but carefully. Despite all the hard feelings it is in your baby's interests that you all "get on well", at least as far as he sees it. It is in his best interest (unless obviously he is in danger) to see his dad. I expect lots have said this before but it bears repeating as it is hard to put into practice.
I think that 9 days 300 miles away is probably too far and too long away from you no matter whether with dad alone or with his DP/OW.
Second problem..As for being matey with the new DP/OW. The above applies. I would keep an open mind about it.
I am on the other side.. a SM to three kids and have none of my own (I was NOT the OW though! They had split up two or three years before we met). We have the kids twice a week and all weekend. We have been on many "family hoildays" ...they are teenagers now.
I wanted to meet my DHs exW as soon as we knew that our relationship was going to progress. Why? I thought to myself..if I was a mum of three kids who had this new person in their lives, possibly taking "care" of them if called on, I would want to know what this new woman was like.
I am not suggesting for a minute that anyone should "vet" anyone, btw. I just felt that it was the right thing to do.
It is still all very raw for you. However I cannot stress enough how important that it will be for your DS to see a smooth transition. There is no need to be matey and friends. I am not friends as such with my DH's exW but we do have a laugh on the door step when the kids arrive and she is always borrowing things from me. We are completely different.
My DH holds much bitterness towards his exW and her DP which I try and smooth over for the sake of the kids. I came into a bit of a car crash of a split (she left my DH for her DP after 16 years marriage, new DP was 15 years younger than her!! My DH cannot now, even 7 years later, bring himself to speak to her new DP).
Your DS is still very young, which is a good thing in a way as he will grow up knowing that dad and mum do not live together (as opposed to a sudden split for a child who has to cope with a new life) and if things are civilised and happy, that is all he will remember. There will also come a time (I hope for you) when you will meet someone new, as happened to me, I was the "new" person who has nothing to do with the break up and you will be managing the same situation from a different side.
It sounds as if you are being very sensible. I can only advise that a calm and steady hand/heart/head usually works in these circumstances XX