Hello S.. I am myself going through this situation. My daughter is also 4 years old. I have told her that right now we are yelling and fighting too much with each other and we both need "time outs". He has been gone now for about 2 months, and one day she told her Auntie, my Sister, that he doesn't love her anymore. So I sat her down and explained that he loves her and nothing can change that, and that he and I just need to learn how to talk and not fight. I used the kids at school as an example. After our talk, my Daughter jumps up very happy and says, "Oh, so then he doesn't love you!" and skipped outside to play!! OMG... kids?!?!? LOL. Anyhow, you know your own kid. It took a few weeks for me to realize that my fear, was just that, MY FEAR. In the midst of reflecting on a lonely night, I realized that she was fine. We both are trying really hard to over come our issues and not use her as a scape goat to getting back together, in fear of raising her in an unhealthy home.
Every kid is different and only you know the sensitivity of your child.
Also, what I have done is picked up the pace and play with her during the after work hours rather then cleaning up. I would cook and clean after work and he'd keep her company. Well now I feel like I've still got to keep her busy so that the effect of him not being there isn't so dampering on her. It's a plus because I get extra hi-fives and memories with her, but YIKES!! my house isn't as tidy as I'd like it to be. . . LOL.
I wish you the best of luck. My heart and prayers go out to you and the little one.