get an alibi
Legally, a widow is someone who has lost a partner that they were married to.
Once your husband dies, the marriage is no longer valid. You may marry whoever you like.
If you are separated but never took the steps to divorce, you in general would inherit all property.
Yes, unless his parents claim it because since you weren't married to him, it is not legally yours to keep.
You need to consult with an attorney who specializes in family law as soon as possible. You are still legally married even if you are "legally" separated. That means if either dies the other would be their legal heir, and each has certain legal responsibilities where the other is concerned. If your marriage is over (as it would seem if your spouse is living with a new partner) you should take the necessary steps to end it legally so that you can move on with your life and find someone who wants to share their life with you.
Not legally since you never actually divorced him
No. Unless you can prove that you paid the mortgage during that time, and that will take some hard work.
The length of the marriage is what usually determines if a spouse or ex spouse is entitled to any pension benefits either private, SS or RRB.
he dies
He dies, he stops living.
When a living thing dies, it dies. Thus, every living thing has one life.
No. He cheated and dies.