Jeremy married sarah, who belongs to the same ethnic group as him. additionally, she is a christian like him. in this scenario, jeremy is engaging in bigamy homogamy hypergamy exogamy

In the scenario in which Jeremy married Sarah, who belongs to the same ethnic group as him and additionally, she is a christian like him Jeremy is engaging in homogamy. Homogamy is marriage between individuals who are similar to each other (in cultural sense, in social sense..).
The fact that Jeremy and Sarah are both Christians and belong to the same ethnic group means that they are very similar to each other.