My heart breaks for you but you're right, think of your children. I've been at real lows, I have a good network of friends whom I can really open up to or just cry to and this is a massive help. However I've learnt to choose my friends wisely and who I say what to. What you want is validation and the ability to offload, some friends can just want to protect you and then up being nasty towards your S, as much as they're hurting us, they're still our S and for all their faults we still love them (or we wouldn't be on here).
Find someone you can talk to so that you're not bottling this up yourself. I found the beach to be a place for some good mind emptying and a playlist of a mixture of strength building songs (I will survive etc) and some to open the floodgates and have a damn good cry to. We're allowed to cry, away from the H/W is obviously best but don't keep it all in, it'll just be like a bottle of soda that you shake and shake until it explodes. Find an outlet, I bought a punchbag!
Have you gone to your own therapy? Not marriage counselling but to rebuild you? There's no shame in asking for help, it'll only make you stronger and that, in turn will help your children. My D is 18 so I don't have the same custody concerns but even though you're feeling low this doesn't make you less of a parent, it just means you care and you want happiness and stability for you all. Asking for help is far better than being in denial and burying your head as a lot of MLC S's do.
Look after you first, someone told me it's like the warning on the plane, put your own oxygen mask on before you try helping someone else, you're of little help to someone else if you can't breathe yourself.
You're not alone
Me: 38 H: 40 (39 @ BD) BD: August 2015 T: 22 years M: 15 years D: 18 years (17 @ BD)