Is sincere repentance from grave sins, such as removing the hijab and marital infidelity, acceptable to Allah, and can the relationship with the husband be mended after these events?

What you have done are grave sins, but the door of repentance is open. The conditions for repentance are: regret, ceasing the sin, and resolving not to return to it. You must ask for your husband's forgiveness without explicitly stating the betrayal. The reason for what happened is weakness of faith. You must mend your relationship with your husband by listening, obeying, and showing affection. If your husband's utterance was a kinayah (allusion) and he intended divorce thereby, then it is valid; otherwise, it is not. We advise both of you to read fatwas related to resolving marital problems. We also advise reviewing fatwas regarding the ruling on a woman's work, knowing that your sustenance, your child's sustenance, and your housing are the responsibility of the husband.