Hurt and need to vent

So, my partner has a little boy with his ex and it's been a very long crazy ride.

Shes tried to get him thrown in jail to win custody of their son with false allegations and has over all been very hard to cooperate with civically. But to this day I've been nothing but pleasant and have been supportive and tried my hardest to show to her I am not trying to steal her son.

I miscarried last year and would have a 5 month old child today but unfortunately i dont. It hurts, it hurts so bad because i do want children of my own. And it hurts to be reminded daily I am not a mother.

I love my partners son like he is my own, but i am not trying to take his mother's place- I'm just trying to be a role model he can grow up and look up to when he needs help he feels he wont be able to reach out to his parents for. (As a child growing up with a broken home, i understand this is a possibility.)

She doesnt want me around her child, doesnt want me holding him or speaking to him even though he lives with my partner and myself and I do help raise him and take care of him. I feed him, clothe him, change him, play with him, and console him when he cries. It just hurts to always be reminded I'm just the other woman who doesnt have children of her own.

My partner gave me permission to post this picture (below) of us on my Facebook and apparently she through a giant fit and everyone is telling me that it was wrong and hurtful even though it wasnt my intention and when my partner asked me to then remove me without really any context and I asked why he got upset with me and when he tried to explain when it comes to his son I have no say in any matters and I have no connections to him to care about.. but I believe that's wrong of him to say because I do help raise him, and we are bonded and hes told me several times I do have a son vicariously through him.

Again I'm not trying to replace his mother but it was just more salt into the wound I already have and it hurts and makes me feel very insignificant even though I'd do anything for that little boy. And now I dont know what to do because if a picture was so wrong.. it makes me feel like an intruder for feeding him, bathing him, changing him, playing with him, and holding him to console him when hes crying all night.. It makes me feel like I need to pull away because I'm crossing a line..?

Im currently in my 2week wait to take a pregnancy test but it feels like I'm never going to be a mother, never going to give birth, never going to give my love to my little one. (I love his son like he is my own and when I do if I ever do have a child they will be loved equally and no favoritism.) It just hurts. Does anyone else know what I'm going through..? Words of advice? Help. .