How do I get over feeling this way?

My husband and I have a 2 month old. He has a daughter from a previous relationship. I knew this before I got with him and I could never hold it against him for having to pay child support but, we are going through a tough time. We are living with his mom and he left out of town for work to make more money so I've lost my husband. He said he would start giving me money to say up so we could put down for first months rent and deposit on an apartment but he told me he has to pay his child support out of this check. I know that's something he can't avoid. I'm not mad that he is taking care of his responsibilities but I just get tired of feeling like me and my baby will always come second to his first. Like here I am alone crammed in his mothers house with our son and no money and i get to watch his ex have a 3 bedroom house and nice clothes and be a bitch.