All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If the matter is as you have stated in the question that your husband had left you without leaving any provision for you, then he has indeed committed a great mistake. That is because the husband is responsible for his family in the Sight of Allaah and he will be held accountable for it on the Day of Judgement. The Prophet said: "The husband is a guardian of his family and he will be questioned about those under his guardianship." [Al-Bukhari and Muslim] The husband is also obliged to spend on his wife according to his ability. Allaah says (which means): {Let a man of wealth spend from his wealth, and he whose provision is restricted, let him spend from what Allaah has given him.}[Quran 65:7].
We advise you to endeavour to get the news of your husband so that you would be able to contact him and make an effort to reconcile with him or ask him to divorce you. If you are not able to contact him, then in our view you have to take your case to the brothers who are running Islamic centres in your country, because the issue is that of the wife of a missing person and the scholars differed about the rulings that apply to this issue. For more details please refer to Fatwa: 83671.
It should be noted that you are not permitted to marry another man until your marriage is nullified or that your husband appears and divorces you. It is absolutely forbidden to take a friend whether you are still married or not married, and it is even more evil and forbidden when you are still married. Committing adultery with this man is a great major sin, so you have to repent. Allaah says (which means): {And do not approach unlawful sexual intercourse. Indeed, it is a Faahishah (i.e. anything that transgresses its limits; a great sin), and an evil way (that leads one to Hell unless Allaah forgives him.}[Quran 17:32]. Besides, you have to end any relationship with this man; if your husband is neglectful of your rights this does not permit you Islamicly to add to his mistake with another similar mistake.
Allaah knows best.