Did you say 60/40 in favor of you and she "missed" 20 days of her parenting time with the kids in 2015?
I'm glad you are keeping track. Journal/diary this stuff indefinitely.
Your kids will one day reach an age where they will choose to spend more time with one parent than the other. Being primary custody parent is an advantage but you also want things like living close to all their friends and being active in church to help push you over the top. You should always be preparing for the opportunity or maybe the responsibility to protect your kids from your ex-wife's detached, selfish, destructive and unhealthy ways. This OM or another OM might someday get creepy with your kids and having a huge catalog of evidence all ready to go of how you've already been the primary parent for the most part for 2, 4, 8 years will help you win your case.
I know it's not your long term goal right now. You are still getting your feet under yourself. But being pre-prepared for the chance you might need or want to act is wise.
Also - when your kids are teenagers they can really choose where they want to live and that'll most likely be you....the only parent that puts their needs about his/her own.
I'm also not saying this to be vindictive towards your ex- but introducing them to the person that played a part in destroying your family doesn't bode well for her being or becoming a great parent EVER. Like TX doesn't think letting OM off the hook is a good idea (I agree), I don't think letting way wards raise children is a good idea either. Your kids would be safer with you. If you can use her illness and ineffectiveness against her....you may want to try earlier than later to modify your custody order. Don't just let the kids spend "her time" with her parents because she's too sick to handle them. Instead of 20 days she misses custody - go for as many as you can get and document it all.
I'd also recommend that someday, if OM sticks around, that you warn your kids about him and let them know he's the guy the broke up mom and dad and split up their family. Kids need the truth to protect themselves. It's may feel better to conflict avoid and think it might be harmful to say that to young children but I'm of the belief that the truth and need to know overrides lying and covering up things. They will be more harmed learning the truth later and thinking back to all the gifts, hugs, kisses and time they spent with the OM (step dad someday). Honesty is the best policy. If and when your kids ask....tell them the truth. Expand where necessary. Just as you can't tell her who she allows to sleep over - she gets no say on how much truth you share with your children.
The internet is 90% complaining and entitlement and I hate it because I deserve better!