More acceptable today than when? Currently in the US, the vast majority believe it is an unethical betrayal of trust, but 75% of men and 68% of women have cheated at some point in a relationship. Masters and Johnson were the first to compile statistics on sex beginning in the 1950s, but I don't know if they ascertained cheating determined percentages.
You also need to define cheating. A percent of women think their significant other looking at pornography constitutes cheating. Bill Clinton was receiving oral sex from Monica Lewinsky but was adamant that he was not cheating because in his definition only intercourse qualified. Lastly, many couples are open or swingers and discuss and agree to terms and conditions where the other is free to have intimate relations outside of theirs. It's not exclusive or monogamous. While that includes any sexual act, the parties do not regard it as cheating because it was agreed to and therefore not a betrayal.
Men are hard wired to sow their seed and spread their genes. But humans have free will to exercise discipline and self control. Females used to be selective because they wanted the best genetic specimen procreated in their offspring, able to function in modern society, and they wanted long lasting support from a male partner. The very word "adultery" comes from adulterating the bloodline, and having some other guy support your kid. All that is out the window in the US today. The pill and safe abortions make women unselective, and if they do have kids the Dad doesn't need to support them. There are myriad government programs that will pay to raise them. Eighty percent of blacks are born out of wedlock. Most are born on Medicaid or now obamacare, raised on WIC and foodstamps until they get into Headstart and the free lunch program, which today has expanded to lunch and breakfast. There is no consequence to being irresponsible. Democrat politicians love irresponsible voters addicted to government handouts, because their vote counts as much as a responsible taxpayer. They try as hard as they can to encourage them and increase their numbers, because it keeps them in power.
You also see from the Obergefell v Hodges Supreme Court holding that same sex marriage is now legal. While lesbians are generally monogamous, the average male homosexual is wildly promiscuous with 83% citing more than 50 partners, 43% more than 500, and 28% more than 1,000 partners. 79% of the partners were strangers. That was an argument, albeit unpersuasive on this court, that homosexual recognition makes a mockery of marriage and a holy union.
All relationships are unique. There is less and less a standard template. You need to communicate your expectations and find a person, trustworthy, who can agree with those terms.