Even if you just go out for a walk... smile and say hi to people as you pass them by, it will make you feel better inside...

You are acting as a full time parent to your DH's kids. One of them is 3 years old, Good Lord you have my sympathy, so your are a full time nanny to your SH's two kids. You take care of the house, cleaning and cooking, and laundry. Does your DH help with any of these chores, does the 9 year old have small chores, heck, even the 3 year old can help pick up toys and such. If you go online and find out what the cost is for a fulltime nanny, a house cleaner, a cook and if you took all your laundry to a service, you will find out that you are contributing WAY more than your DH. 

Don't be so hard on yourself, and if anyone blasts you on here, just flip them the bird and scroll on to the next reply. Life is too short to deal with a$$holes, that do not know your life. Yes, we can be very blunt and some of us come across as being mean, but we too have step life situations that has turned us this way.

As Kaylee said, go for a walk, since everyone is wearing masks, wave to people and say Good Morning or Beautiful Day. You will be surprised how many people with respond or are just as lonely as you.

There are two issues here that you are blending into one.

First and foremost is your mental health. There is being an introvert and being disconnected from the world. It sounds like you're dealing with the latter, with perhaps some depression (you're not eating and you don't "seem to care" about much) and maybe anxiety related to be abandoned by your family. I'm not a therapist, so these aren't diagnoses. But, you're dealing with a lot, dealt with a lot, and don't have an outlet. YES, you need friends and companions outside of two children and your husband. What has caused you to think that you don't?

Second, the kids likely enjoy staying with you all more BECAUSE you have rules. Yes, kids push boundaries, but they also learn when they do that, either something good or something bad. They want that stability that comes with rules. 

As an example, your house has a bedtime. Let's assume BM's doesn't. Your DH tells the kids that they need 8 hours of sleep or they'll be tired and grouchy, and then they'll get in trouble at school for falling asleep at their desk and being mean to their peers. BM never says anything.

So, before DH ever had that conversation with them, BM let them stay up super late, and the kids did. Every day at school, they kept getting in trouble for falling asleep and being little grouches. Well, BM never said anything or corrected the bedtime problem, so the kids start just assuming they're bad kids.

That is, until Dad delivered the piece of golden information: they NEED sleep. All of a sudden, they are awake and happy at school! They realize they aren't bad kids. They may not like missing a show because they have a bedtime (because kids don't like missing out on fun), but they certainly like not being tired and angry and in trouble all the time.

Kids need structure. But they also need structure from their PARENT. That would be your DH. HE needs to be helping with homework, drawing baths, putting them to bed, making them their snacks, waking them up for school, etc. You can handle all the household chores like laundry, mopping, cleaning the bathroom, etc if you want to help your DH. When it comes to his kids, though? HE needs to do it even if he's tired. That's HIS JOB. HIS RESPONSIBILITY. 

EVERY parent is tired. It's a tiring job. You know it because you find yourself tired. It's doubly tiring for us SPs because we don't get the same gratification for parenting these kids as their parents do. The reward just isn't the same, and that reward is what pushes parents to give their all.

It's a myth that SPs have to love and treat their SKs as their own. I feel like, parricularly for SMs, that's a cop-out for the actual parent parenting poorly. "Oh, he wouldn't be such a terror if his SM weren't so mean to him!" Well Karen, either Dad didn't teach the kid to not be a litte goblin to his SM OR he was so entranced by her vagina that he let his son suffer under the tyrany of his wife. DAD has the responsibility here and DAD is failing, not SM.

Anyway, get a handle on your mental health first. Get into therapy and sort through some of the emotions you're feeling (or can't feel). Then join an online book club, take a socially distanced art class, volunteer somewhere - do SOMETHING so you meet other adults and have a group of friends who aren't your spouse and small children. 

At the same time, reorganize household labor. The kids fall on your DH. No matter how you divide up household chores, the kids are his. That doesn't mean you CAN'T help with schoolwork or make a snack for them. It just means that you get to CHOOSE when you do it and your DH is the default provider, not the other way around.

And if you tell me that he just leaves them with you all day, put an end to that by finding daycare for them. First, the kids need to learn to socialize just as much as you do. But most importantly, you're WORKING. You don't have time to step in and take care of them while working, not when they are that young. If DH can't take them because he's working, then the same grace gets extended to you. It may be expensive, but your DH chose to move closer to his kids and hasn't enforced the visitation schedule (which I debate on whether or not he should, unless he's paying an obscene amount in CS based on when he's supposed to have them, but that's a different topic), so he needs to make sure they have ACTUAL child care. You're not actual child care, you're his wife and an employee who needs to be able to work with other adults at an adult level.

You are not alone in feeling lonely.  You seem like a kind person who has allowed themselves to be dumped on.  You have overnight been put in a parental role for kids that aren't yours.

Why are the children being given the control here? Unless abuse is suggested, why is your DH not sending them to their mother?

That would be my first hill.  It's wonderful they like you and never want to go back.  But tough banana cakes - they need time with their mom.  If they are being abused, then your DH - not you - need to get on that with CPS. 
 

With this great new arrangement for everyone but you - has your DH pursued custody and lowered CS?  That would at least allow him some funds to hire a cleaning person and/ or part time real nanny/childcare to take the burden off you.

Also, please stop feeling so sorry he's tired from a physical job!  He wasn't so tired to make 2 kids with an ex less than 4 years ago.  He is the one who needs to be responsible.  He created them and needs to man up to their care - if not himself them through hired help.  Instead, you , due to a kind and caring nature are unfairly being taken advantage of. Life is great for him while you cook and clean and take care of his children.  He's 100% taking advantage of your good nature. 
 

He is not as good of a spouse as you are to him.  Now he has you isolated, friendless and seems happy to alienate the kids from their mom by constantly keeping them with him, while likely paying his ex CS to not take care of the kids they had together.

You are in charge of the life you want.  If it's not unpaid caretaker and maid to kids that aren't yours, you need to say so and demand your DH figure it out.  Insist the children leave the house during moms time.  As the old saying goes, you don't have to go home but you can't stay here.

Those kids are being given too much control, you are being taken advantage of and you deserve better.

All of this is being said with love.  You are a very kind person and it's biting you in the behind.
 

When they ask to stay with you, say, "No, it's your Mom's time, she really loves you and wants to see you - it's important that you go spend time with her."  Stop letting little kids drive the custody schedule, and stop taking over all the parenting for your husband.  If he's too tired to handle them, then he should reduce his custody time.

You are being much too kind to everyone in this scenario (BM, DH, skids) and not kind enough to yourself.