This might be long so bear with me.
My dad has been with his partner for fout or five years. It took a long time for me to meet her - about two/three years. This was partly because when my dad told me about her I said I didn't want to know as my parents had only been split up about six months. I was 19 at the time, at university and really struggling with my mental health. I was depressed and have always struggled with social anxiety.
After around a year of me 'knowing' about this woman I said I'd like to meet her and it still took another year because she kept cancelling on any arrangements to meet up.
She's a nice enough woman and my dad seems to love her very much. She talks very little when I am around her and in total I've probably only met her less than 20 times. Until last year I'd never met her kids. Again arrangements had been made multiple times to meet them but these were cancelled (not by me).
My family home was finally given an offer in November last year after being on the market since my parents split up. On Boxing Day I turned up to see my dad as arranged knowing that this would be the last time I was in my home of 20+ years to find that her kids were there without me knowing they would be. Me and my DP arrived to them already settled in, one of them already settled in to my childhood bedroom and my dad hadn't told me I couldn't stay that night. I probably came across as very awkward and uncomfortable and I did have to leave the house to have a small cry on the street as I found the experience overwhelming. They were aware that me and dp were attended and so had bought us gifts. We were not aware and so had only brought gifts for my father and his partner. I felt embarrassed and my social anxiety completely took over. I probably came across as very rude as I hardly speak when the anxiety takes over (too busy having panic attacks). The night was not a complete disaster however as eventually I loosened up a little. I felt worried I'd shown myself up to be an arse and had upset my dad but he seemed ok with it all.
That was the only time I've met my dads partners daughter, I've met her son once or twice since then. However her daughter invited myself and DP to her wedding and I felt obligated for my father to say yes. In hindsight I should have declined.
Wedding was this weekend and it was a disaster for my anxiety. Obviously knew very few people there. My dad clearly has a much closer relationship to his stepchildren as I do to his partner as he has moved far away to live with her now the house is sold. I blindly assumed me and dp would be sat with my dad at the wedding but he was at the top table. We were sat with a group of randomers (I know this is common at weddings but my social anxiety really struggles with 'small talk') and for the whole ceremony I felt uncomfortable as everyone was talking fondly about a bride or groom I'd only met once before. I didn't have any funny stories - I hardly knew them. All the speeches and the table conversation felt alien to me. It felt like hell sitting through it all and I felt guilty that I was runining the day for the bride and groom and other guests as I was so out of place. I had multiplied mini panic attacks throughout the meal.
After the meal I told my dad I was going to lie down in the room for a bit as I was feeling unwell and I didn't know if me and dp would return. I honestly didn't think we would be missed as we hardly know her. I was wrong. My dads partner was fuming the morning after that we had disappeared and the bride and groom felt snubbed. I now feel that after two awful first impressions my dads new family must despise me.
I was completely unreasonable wasn't I.