I don't think you should do it hun, but I don't think you're being totally immature (just a little

), you're angry and upset at the situation and I totally get why. The ammount of childish and immature and spiteful things I've dreamt of inflicting on FOB.. but the point it I would never do it because then that makes you just as bad as them and you don't wanna be that kinda person, especially because you're the one holding the baby so you need to be the one taking the high road for LOs sake as well as your own.
My advice to you hun (and I know it's easier than it sounds) is to try and let go completely. It's not him/his family it's hurting you getting wound up it's YOU and your baby will be feeling the stress too. You need to move on, put it all out of your mind completely and just see it as just you and bubs and I promise you once you start making yourself it'll jut come as second nature and you'll forget FOB was ever part of your life! Like someone else said either get him to sign over his rights or get the money you are owed, legally those are your rights as a mother so they can't do eff all about it.
And as for FOB, if he doesn't want to be part of LOs life then as sad as it is there isn't a single thing you can do about it. The amount of times I've cried just because I feel so utterly heartbroken for Evie that her daddy just doesn't seem to care about her

but who is that helping? No one, especially not her! So you just gotta make yourself the BEST mum
and dad you can be so you can rest assured within yourself that she's not missing out on any love or anything.
Sorry that was a bit long, just I've seen lots of your FOB posts and never get around to replying so thought I'd give you my 2 cents. He's not worth it hun and you'll be fine without him, like I said you just need to let go for your own sake or it will make you bitter

x