Half siblings of child v own children

[traces456]

I daren't post this in AIBU but I want opinions on this please, my partner has a child with a previous girlfriend (never married) of 5 years (split 10 years ago) his DD is the youngest of four siblings who all have the same mum but three different dads, the other dads have never been involved, after they split my partner continued to treated her other children as his own. When we met 3 years ago he told me he had 4 kids, then quite soon afterwards told me that only the youngest is his but they all call him dad. All apart from the youngest they are adults now and still call him dad.
I have 4 children with my ex husband, I feel that by referring to these kids as his own he somewhat diminishes my experience of having given birth and brought up 4 kids of my own, when we're out he would tell people he has 4 kids and I might say and I have 4 kids too but I feel as if even though he's done a great thing by being there for his ex's kids they aren't his kids and it's not the same as me saying I have 4 children.

Please help me understand why I feel slighted by this, I'm probably being massively unreasonable hence posting here rather than AIBU

The only way I could imagine feeling bad about the partner referring to another man's child as his own is if you had a child abandonned by his father and your partner wasn't too involved. That is my situation.
My DP still pays some maintenance to his ex's 21 year old son (who has an involved father who lives in Cuba and apparently doesn't have money). My own almost 13 year old is abandonned by his father, we've been together over 6 years and other than sharing the common expenses, my DP doesn't feel the desire to buy things for him (not that I ask, I just noticed), nor there is much of a relationship (my son being shy doesn't help).

I feel that my son being abandonned by his father and being much younger needed him more than the ex's son who has his father as well as his mother's new boyfriend's involvement, so his involvement somewhat hurts me. If my son had an involved father, I wouldn't care much.

As you are aware YAB massively U. You are diminishing the role that adoptive, step and foster parents have in their children's lives
This ^^ As an adoptee myself, I find your comment very offensive, my parents love me as much as they would have loved a birth child. You seem very jealous of his other children, particularly given the fact that you say you don’t have an issue with his birth child. He sound a very caring and loving man, who has done an anaZing job with these children - what a shame he’s ended up with a nasty, jealous woman like you.