I've "lost it" in front of my kids. They see my emotions and I see theirs. It's just part of life. Sometimes I handle my "big feelings" better than other times. When I don't handle them as well as *I* would like, or when I fear my emotions have made a big impact, I talk it over with them: "It's okay to feel angry, it's not okay to raise my voice when I am angry. I am sorry for raising my voice," or, "X and I felt angry with each other. We still love each other and will continue to love each other", or "I felt sad and I cried. We all feel sad sometimes, its okay to feel sad and cry. I'll be alright, but right now my heart hurts."
I don't think there is anything wrong with being human and a parent. In fact, I think it's important for children to understand that all people have feelings and are "flawed". We still show up for our kids, put food on our table, love fearlessly and unconditionally. They can see us as human, because we are. (Also, while I don't expect my children to support me (especially because of their age) I do want to teach them empathy and compassion. Being real about where I am, what I am capable of and how I move through, is part of that.)
Good luck getting through. These are tough times, but you will make it and your feelings are not forever, nor are your circumstances. Change is the only true constant.
edit to add: While I don't try to put on a face very often, I do try and need to cope in healthy ways. Here's my way:
My Partner works long, outdoor, physical nights and sleeps days - so often he is only available for family time a few moments before he leaves again. I am not able to get help, support or a break on those days. So, when I feel like I am going to boil over or am headed for a big emotional burst (it has been a very hard year), and I really, really need some space I will either take deep breathes and remind myself of the impermanence of the situation and just get through till bed time (grin and bare it, pull up the ol' boot straps mode). My mantra is: I will be okay, I am strong, It's not forever. Then, once the kids are asleep I can take a nice long hot shower and let off some steam.
Or, during the day I'll put on a movie for a couple minutes and take some space while the kids are distracted. Talking it out with a girlfriend during this time, helps me.
The problem with grinning and baring it for *me* is that it can end up taking over. I forget or suffocate the need to properly deal with or process and suddenly feel like a crazy person because I haven't been able to gradually let out my emotions or figure out what's going on. Auto pilot is great for short spurts but not for all the time-everyday life.
Calls to girlfriends and my Mom are of the utmost importance for me. And/or, if I take a few minutes to write or draw, I feel better as well.
When I feel like I have too much of everything going on, I put cleaning, laundry, dishes and fancy meals on the back burner. I do my best and get through and then, when I've had a chance to breathe, I clean up and play hard with the kids.