Trying to be polyamorous, or have an open marriage, when your spouse hates it, and feels like she has NO WAY OUT because of small children and finances, is emotional abuse, pure and simple. (Even though she has a way out even if she is too scared to see it. There is always a way out.)
You either don’t do it, or you separate from that person so you can live the life *you* want to live.
Either of those options is honorable.
Staying married and doing it anyway while your spouse hates it, is wrong.
People should enter into to commitments such as marriage with clear understandings of the relationship. If two people are committing to each other, will they be monogamous? Will they be sharing a third person or a series of third persons – at the same time or separately? Will one of them only have sex within the commitment but the other will also have sex with others – and under what conditions? It is important to have understandings.
However, even with understandings, people grow and change over time and circumstances change. Someone who agreed to monogamy may later discover that they are more suited to polyamory, or vice-versa. As painful as it can be, the right thing to do is to discuss the desire to change what the conditions of their relationship are. If the other person doesn’t want a change, then the person who does should either stick to the existing agreement, or leave. In the happiest of situations, the other person will agree to the change and find it to be a good one.
Violating the agreement is wrong and destructive. In this respect, openly polyamorous people show better character than people who carry on a pretense of being monogamous, but are not. Those who claim to want to protect the sanctity of marriage actually work against that when they point with one finger to polyamorous people as committing adultery while with the other hand preventing them from having more than one spouse.