My advice for what it is worth is to wait until they are all out of the house. I am a widow as well. Self sufficient and a kid that I adored who was thriving. Married 6 years with my now husband and dated for 3 years before that. I didn't rush into it.
But, if I had to do it all over again, I would live in separate houses. Things are great now, but one child sued us and the other one was so neglected by his mother, grades and just social skills are still a struggle.

Do what makes you happy, but know your children need to come first. Mine has, but with some resentment for how this household was after the wedding. All hell broke loose and both my SS17 and BS21 still resent it. As for my SD19, not a part of our lives anymore. They have zero relationship with my SD and hate is a mild word for what they feel. Writing was on the wall, and I warned my husband when we were dating, but the issues he felt was just a high energy child. There are a lot of things he would do differently if he could. But, unfortunately too late and she is who she is. He sees her occasionally now when she is home for college. We are lucky in that she is not costing us anything.

If I could do it all again, I would continue dating and live in separate houses. Maybe then, it all wouldn't have blown up in our faces....I never foresaw what happened.

Don't move in with him. Keep dating him if you want, but your kids deserve a soft place to land and peace in their home. A 18 year old failure a 14 year old boy who has yet to really hit the tough teenage years and a guilty daddy add up to anything but peace.

A year to be dating is very short. Give it a couple of years, let his kids move out, then maybe consider it.

Keep dating but do not marry or live together yet. NEVER marry a person who has a "failure to launch" adult child at home. There is no way to have a happy ending.

A person with an adult dependent child at home is probably worse than a man who has a mistress on the side. A parent with an adult child will defend and enable that child - where as the cheater has to at least pretend that you are more important.

When you marry a person the marriage should be your first priority. That would be a terrible mistake with this man and would deprive your children of a decent life.

At only a year of dating you two barely even know each other. What's the huge rush? I dated my DH for 6 years before we married, and often I feel like maybe we rushed into it. 10 years later we are STILL learning who each other are. You need to slow your roll.

The best environment is a clean, honest, as stress free as possible home. The boys are very close in age and it is entirely possible your son will try to imitate his son in an effort to be cool and accepted. The lack of consequences (you said he's very lenient) may give your kids the wrong idea and the wrong direction.

What you see as "issues" now living in separate households are probably going to feel a whole lot worse, more stressful and more like energy draining craziness when/if you are living with it full time. It is a Very different thing to see messiness, constant manipulation attempts and thievery when it involves your things or that of your children. Blending is very difficult and there are 3 teenagers (almost) at least one you anticipate to be a failure to launch that will make things so interesting with hormones, the desire for things to be fair and normal sibling squabbles.

It's great that you want to have both of you on the same page for co-parenting, but even that can get difficult. If the same page is very far off from what he's been doing so far, his kids will likely resent you for making the status quo change.

I'd personally recommend waiting at least until he gets his kids launched and independent before you move in with him but I agree all the kids should be put before you do this. The difference in parenting styles, levels of guilt, the ages of the kids and their behavior suggests that blending will be stressful and complicated.

You say it's "over a year" so I'm guessing it's less than 2. That means your kids have gone through a major life event of losing their dad within the last 2 to 3 years. That's huge. Going through another with moving in, the the actually process of blending and possibly another if it doesn't work out.... it's a big risk. For me it would be too much of a risk, but you have to decide that for yourself.

At only a year of dating you two barely even know each other. What's the huge rush? I dated my DH for 6 years before we married, and often I feel like maybe we rushed into it. 10 years later we are STILL learning who each other are. You need to slow your roll.

As everyone else here has said, wait.

Do the counselling and see if he does any of the things he says he will. When people are dating they are bringing their best persona to the table. They are agreeable and willing to say or do a lot of things that they won't say/do once they live together.

See if his 18 year old launches or if he enables her. See if he makes them clean up their space. What is he doing about the missing money?

People don't generally change when they get married or live together. If you don't like his parenting now, you most definitely won't like it when you live with it. The biggest thing for you to understand that if he doesn't change before you move in together, he never will.

I'd consider waiting, go to counseling and keep this thread in the back of your mind. Your children are so young that I would be doubly cautious. I suggest keeping separate households for the next year of two. Don't rush.

If I knew what I know now I would have never moved in.

My hairdresser and her boyfriend are waiting until their kids are grown to move in together . She has all of the benefits of a fun relationship and none of the step kid work or drama, non if the birth parent crap and none of the in law crap. Her kid can grow in peace. Much smarter decision, imo. They've been going on strong for 5 years.

Do you really want to partner with a man who will help raise your children and has produced the near adult aged children you describe?

You bit on the first fish you engaged with in the pond. Give yourself more time. Set your personal value much higher and the value of the quality of character in a partner that you will espose your children to even higher.

I get that you are lonely, that you lost your mate, and that you think you need a partner. You don't need a partner. You want a partner.

Two very different things.

Take care of you, and take care of your kids.

The partner thing will work itself out if you value yourself and your kids appropriately and hold any suitors to that standard. Don't accept a partner who has spawned and raised children to near adulthood who are "lying and manipulating. There is also a question of theft (money missing from wallets). They are lacking in general manners and cleanliness as a result of their poor relationship with their mother and overall family history". Their father is arguably the biggest influence on them and they turned out like they are.

That is not the partner you should be selecting to be your equity life partner and to help raise your children. Even after his children launch he is still the primary parent that raised them to be the less than desirable people that they are. If you cannot be more selective then forego dating until your children launch.

IMHO of course.

I agree with Rags. "Take care of you, and take care of your kids."

Nothing and no one is more important than YOU and YOUR CHILDREN.