I'm a little confused. You say it's "unrightful" child support, but if it's ordered by the court, then that's what he has to pay. Some states require CS to be paid with a 50/50 agreement, some don't. Most states will also require him to pay for half of child care. And he needs to get caught up on arrears. 
 

I don't understand what BM paying for another kid has to do with his child support, it shouldn't be a factor. Also, he needs to stop doing BM favors by letting her have tax money.  If he feels the order is unfair he can go back to court to have it reviewed. 
 

Part of being with a guy with kids is that he has to support them - but he shouldn't be paying anything beyond what he's ordered to pay. 

CS doesn't take your tax return or your driver's license unless major arrears are present. How did he fall so far behind?

CS is a calculation. It looks at BM's income, DH's income, and the number of overnights between them both. It outlines who claims the children on taxes and what years and it outlined extra expenses like out-of-pocket medical, health insurance, and childcare. If BM needs childcare, they will grant her some funds toward childcare, but they will also give your DH a credit for his childcare expenses, if the child can't use the same daycare at both households, so it might not give BM half of those expenses. 

DH needs to stop paying for extra things, but he can also be financially stable while paying CS. It sounds like he may need a CS review and/or a different job if it isn't paying the bills. BM paying CS has nothing to do with DH paying CS and wasn't a factor in that court order, I can guarantee that. Trust me, I have my own opinions about the shortcomings of the CS system, but mine are more based on PAS and withholding to maximize CS, rather than having to pay it. With CS, it usually is what it is and is based solely on a calculation. 

I think what you're saying is that on paper it shows 60/40 which is why he's paying Child Support.  But in reality it's 50/50.  So you have two choices - thank your lucky stars that he's not fighting for time with his daughter and consider the money well spent to ensure he's not getting held to the existing 60/40 agreement.  OR go back to court with several years of proof that it's been 50/50 for all this time and you want it formally recognized.  In Ontario, you may still end up paying CS, even in a 50/50 situation, but it's usually offset (both families calculate what the full support would be on their pay, and then who ever's is higher pays the difference).

And if you're going to be in court to show that you've had 50/50 for 3 years you may want to change the schedule.  Personally I'd wait another year until she's ready to go to school.  Then you can say that she's gotten older, you've had 50/50 for four years, and you'd like to switch to a more conventional week on week off since she's now old enough to be away from each parent for longer periods of time.

I agree with others that child support it's just a bill you have to factor in, like car insurance. It's going to exist the kiddos whole life. Even at 18 I'm sure he will be expected to contribute to college in someway or whatever certificate or degree helps her launch. Financially providing for his kid just has to happen.

now if incomes or custody amounts have changed, totally go in for that review that was mentioned above. If that's the case, then the sooner you file, the better.

it's too late to address the tax credits probably, but couples that are divorced and get along that I know of have set up 529 college savings plans for kids or applied it towards daycare and each saved the money. Of course that's people really getting along and willing to do what's best for the kid, and despite your claim in your last post that things were civil things don't seem civil.

also, I noticed in your last post that you're already parenting for your partner. And he's not a very good dad. It sounds like you have for the majority of the time, and that means this child is not being parented the majority of the time. Do not try and fix this man's financial issues. You can pass along our advice, but that these are his issues to fix. Do not pay his bills for him. Do not use your own finances to backfill his situation. It will end up leading to resentment in the long term. And besides, you need a partner not a project. 

I understand your frustrations.  I think CS amounts are often times really unfair.  My husband was at one point paying $750 per month for CS when he had 50/50 custody because BM placed SD into a daycare that was ridiculously expensive, but she know my husband would have to pay for 67% of the cost so she didn't care.  At the same time, he was also paying 4 or 5 hundred a month for his own daycare for SD and for her health insurance as well.  Now that SD is older, the child support is more reasonable and manageable because she is no longer in daycare. 

I agree with the others that he needs to stop letting BM claim the taxes if it's his year to do so.  That's a huge mistake.

This guy is not worth it. Go live your life.

if he doesn't do anything to change it, you're worrying about a dead issue. 

For his ex wife.  He is letting her walk all over him. Walking over him is also walking over you.  Looks like he cares more about the ex's welfair then your family's well being.  Unless you make a stand,  telling this sh*t must stop or else. It's going to continue. There is no reason to give BM all the tax money. 

You must go back to court. You have 50% of the time or more.  BM should be paying you CS.   You must insist on DH taking BM back to court for CS reduction or having BM pay you.  See what DH reaction to that is.  If he actually goes to a lawer or just gaslights you.  Then you know where you stand in this relationship 

Your husbands sounds like the type who just goes with the flow and doesn't understand how CS works. He continues to make bad decisions regarding finances and custody, and now that affects YOU, too.

Can you tell us a little about how you handle finances as a couple? Because it sounds like you don't have a complete picture of his finances and aren't working as a team to tackle his problems. For example, him agreeing to let BM claim SD on her taxes without discussing it with his WIFE first was a big fat no no. Him losing his license due to arrears is very serious and he must have ignored multiple notices warning him to address the issue. Him ignoring the fact that having so much custody of his daughter is a golden opportunity to have his CS reduced is just idiotic. Is he young? Immature? An immigrant who doesn't speak English well? If you plan to stay with this guy, you need to get more involved and make him more afraid of you than he is of BM. You need STRUCTURE and a FINANCIAL PLAN.

Documenting stuff is just a fact of step life, and he should be keeping a calendar of when he has his daughter and only communicate with BM in writing. Compile several months worth of data, then he can go back to court for a review of cs. Get that CS lowered, but continue to pay the former amount until the arrears are paid. 

Come December, your H should notify BM that he WILL be claiming SD on his taxes for 2021, and why. 

I don't know if I could be with someone who handles their business so poorly, or is still his ex wife's puppet. Nor would I want to be the only adult, screwed over by and having to clean up my partner's real and metaphorical messes. You need to think hard about whether this guy is good enough for you, or if you can be happy living this way. As John Wayne once said, "Life's hard. Its harder if you're stupid", and your H hasnt learned that. At minimum, you need to exert more control and require more of him. Put a boot up his butt and some fear in his heart so he understands he could lose you if he doesn't get his poo together.