Is the husband sinful for expelling his wife from the marital home and refusing to support her after her expulsion, and for refusing to allow her to return? And is he entitled to conceal his previous marriage and children when proposing to her?

It does not appear from what was mentioned that you have committed a sin. If your husband has forsaken you and failed to fulfill your rights, then he is sinful, for the Messenger of Allah, peace and blessings be upon him, said: "It is sufficient sin for a person to neglect those whom he supports." It is recommended that wise people intervene to reconcile or to separate amicably, in accordance with the Almighty's saying: "And if you fear a breach between the two, then appoint a judge from his people and a judge from her people. If they both desire reconciliation, Allah will cause agreement between them." He is not obliged to inform you of his marriage to another woman unless he knows or strongly believes that you would not approve of it.