The family you affirmatively created is a little more than just a "problem". It's a responsibility that you took on and can't just abandon because a shiny object has captured your attention. This woman at work has no interest in you and it's not her fault you and your wife decided to get serious as teenagers. When you decide to marry someone you've dated since high school you tacitly agree to forfeit your free and single young adult years. That ship has sailed. Besides, this coworker is off the market and if you can't stop creeping on her you're likely to destroy your career.

If you and he didn't have any kind of agreement to be monogamous in this "situationship" then he's guilty of lying to you but not "cheating" on you. Whether he's "cheating" on this other woman depends entirely on the nature of their relationship. If they're not exclusive then him being with you isn't "cheating". But obviously if he's promised monogamy to her then he is "cheating" in also sleeping with you. This guy sounds like a pig, sorry. But no, don't tell his girlfriend. Just refuse to see him or talk to him anymore. In all likelihood she won't believe you anyway and then you've made this (seemingly duplicitous) man into an enemy. The potential for him doing some revenge seeking on you is too high to even bother with this. She'll figure it out eventually because people like this guy don't tend to change.

Dig up the stats on what it would cost in your area to pay someone to do all the household chores you're doing. Then when you and he sit down to hash out your monthly budget present those numbers to him. Relationships work best when both parties feel they're each providing half of what it costs a couple to live. So negotiate it. Also, don't blithely trot into marriage until this is completely resolved. That includes the future, especially if you're hoping to have a family. It's just a fact that kids will damage your career more than his. So if expectations and a firm plan haven't been established you'll just end up with a lot of resentment. Arguments about money cause more divorces than any other reason.

Always bear in mind that anything you transmit digitally could end up all over the place. So if you have some kind of sensitive job, specifically working with kids, you don't want your face to be seen in any of these nudes. Doing nudity over vid chat is statistically safer than sending pics.

TBH, OP, you don't really sound ready to be married. Maybe get into some talk therapy to cleanse your present of your past (since you mentioned having been cheated on twice just in this brief question). It's never fair to drag your history into a current relationship. But that said, don't marry someone you distrust this much. She may be entirely innocent and you may be out of your mind, who knows. You just can't blindly tie the knot here when you've got all this unresolved angst from the past AND you also think your betrothed might be cheating on you. Good luck.

It's not a pathology to need time alone. It's the people who can never be alone who have emotional problems. What this means is probably that she wants something casual that's nonbonding and not necessarily monogamous. If you need a solid commitment you're unlikely to get it from her. Good luck.

The older someone is (assuming they have experience commensurate to their age) the less time it can take them to make such huge, lifelong decisions. But then there are people who say this to everyone they date. Some of them will be blowing smoke because they think that's what their partner wants to hear. Some of them will just be emotional basket cases who fall hard for everyone. Only time will tell.