On remarriage after divorce or after being widowed, the Rebbe's guidance:
Concerns about marrying a divorcee are generally unfounded today when all the other qualities are there (IK 2846).
For someone seeking a new match after divorce: the search can be hard, so strengthen trust in Hashem's timing, keep growing in Torah and mitzvos, and make sure there is full forgiveness with one's former spouse (IK 2568).
After losing a spouse: alongside faith in techiyas hameisim, one should also take practical steps for one's own and the family's wellbeing, including considering remarriage when the time is right (IK 10058).
Where age and a previous divorce are part of the picture, examine one's own motives honestly; if outside considerations are not driving the decision, proceed with confidence (IK 10494).