AITA for telling my dad he isnt in our life enough.

A bit of context. I (17F) and my autistic brother (15M) live with my dad (51M). Last August we all move to a new house in a village which is about a 20 minute drive or an hour half bus to the nearest biggest city.

Everything was going great until he met someone at the beginning of december last year. His partner is a very lovely person and when we see each other we get on well. My only issue is my dad is never home with us ever since last Christmas. Last month he was only home 6 days and only stayed the night 2. Each month is the same with him only being home for 2 hours this month (to my knowledge at least). It was his birthday on the 2nd and he only came home for 2 hours before going again which really pissed me off because i made dinner and my brother was excited waiting so he could sing happy birthday with the cake i bought and presents (which i now regret buying as in total the cake and presents cost me around £50 which for me is a lot to spend considering work part time). He didnt even eat the dinner i made and instead went in the garage to work on his motorbike. After my dad left my brother cried asking why our dad didnt stay and i didnt know what to tell him.

I understand my dad is old enough to live his own life however i dont find it fair how im acting more like a parent to my brother than he is. I messaged my dad telling him how it wasnt fair he couldnt even stay for my brother and he needs to step up. He messaged back saying that he works his ass off for the house (which i agree is on the pricey side at rent being £1200 a month) and how he struggled to find love and hes finally happy. I said i understood that but said that he sees his partners kids more than his own kids (which is a low blow but is very true) and how its not fair that im having to act like a parent to my brother because he isnt there when hes supposed to. He read the message and didnt reply as has not been home since or messaged neither me or my brother.

So AITA for telling my dad he needs to step up?