Condoms alone are not reliable as birth control. If you are unsure what to use, the school clinic, a private medical practitioner or an agency that deals with birth control will be able to direct you. But my wife is constantly comparing me to her first husband. I'm ready for a divorce over this. It is unclear from your letter whether you have tried to talk with your wife about this problem.
Some people find direct communication difficult or uncomfortable, so they avoid it.
If this is you, I would have a talk with her before you decide on divorce. It hurts my feelings and makes me angry. From here on, please don't do that anymore. You might also encourage an open discussion about specific sexual requests that either you or your wife have for each other, and ask that they be discussed tactfully and respectfully. Most people are never taught how to have sexual discussions, so they flounder and often make a lot of hurtful mistakes.