Am I️ being selfish?

Going on 3 years I️ have tried for a baby with my SO! I️ was diagnosed with PCOS and given fertility meds which also failed. I️ came to the conclusion that I️ just need to lose weight. My SO is 31 and I️ am 24. He has 2 children from his previous marriage that we take care of as he has full custody. They are 9 & 6. I️ love them to pieces. Recently, it has been so heavy on my heart that I️ have not been able to conceive my own child. When I️ talk to my SO about it he just says “Well we have 2 already even if they aren’t yours, they are still yours.”. True enough. He also says jokingly says “I’m not getting younger I’m not trying to be 40 chasing around a 2 year-old.” But I️ know he is serious.

I️ still want my OWN! I️ get so tired of hearing people tell the kids “Oh you must get that from your mom!” Or “Omg! Your step-son looks just like his mom and he sings like her too!” I️ am tired of my SO saying to his friends “I️ got my 2 kids, a boy and a girl when I️ leave this Earth I️ have someone to remember me by.”

Or when Mother’s Day comes & they hurry and call their mom to tell her happy Mother’s Day or they buy her a gift (Yes we give them money to buy her a gift, I’m not hateful like that) & they tell me nothing unless my SO tells them to.

My step-son has even said “You’re not going to have a baby, Mom, you have been wanting one forever and still no baby, just get a doll or a puppy it will make you feel better.”

They are kids I don’t let them know they hurt my feelings. My SO tells me they love me (he too was raised by a step-parent) because if they didn’t they wouldn’t call me MOM (we don’t make them they do it on there own) & that as they get older they will learn to appreciate me.

IDK, I️ just want one to call my own. Is that selfish?