To answer more specifically about SDTs, I would suggest you use protection with anyone you're casual with, and for more serious relationships that you use protection until you all
get tested and show everyone the results.
Then it might be a good idea to get tested again regularly.
is a form here than can help you with that (everyone needs to fill there own).
Otherwise, establishing boundaries is fair. You need to discuss and find boundaries that you are both okay with, and that can be the hard part.
You're a stay at home mom, and that's your job, you say. But whatever his job is, I'm pretty sure when he gets home he's off. And that he gets days off every week. And paid vacation. As a SAHM, you don't get any of that. You're on duty 24/7, and that's not fair for him to expect that from you.
So I think it's definitely fair to ask him to pick up some of the work so you can have some time off as well. You shouldn't have to pay to get time off (paying a baby-sitter for instance).
Having "your" night out once a week is certainly not that much to ask for. It wouldn't even be for the whole day! He had these kids too, and he should take some responsibility for them. A baby-sitter should only be considered if you're having a date out together, if one of you is at home it's normal for them to take care of the kids. And while it wouldn't be fair for you to dump it on him all the time, it's fair for him to share.
Let's look at it that way: while he's at work, your job is to take care of the kids. So if he works 40 hours, you work 40 hours taking care of the kids and the house while he's at work. So far so good, it's equal.
Once he's home though, if you keep working and he doesn't, it isn't fair. What's left of the work should be shared between the two of you.