Need some help with my relationship

Ive been with my man for 5 years and engaged for 2. We started off really rocky and then things got better after we dealt with some issues that happened. For the past 6 months things havent been very good. We have been arguing alot. I know we are both stressed out with work, taking care of my step child, dealing with all the things his ex has been doing and putting my step child through, and dealing with court for custody. We just dont have that spark anymore. We just seem to annoy each other and argue all the time. The only time we get along is when my step child is with us. We parent very well together and take care of her very well. We have fun when she is with us. When she is gone its like we are miserable with each other. We dont have much money to go out so we tend to do our outings when we have my step child so she has fun with us. I know we both hate the fact that we havent been getting the time with my step child that we used to have before her mom filed for full custody because her mom limited our time and im sure that has a part in this. I just want us to be happy again. What can i do to help get us back to being the way we were?