I just saw you were in South Carolina --my apologies, as that will change my answer slightly (I was looking at another state's laws because I misread it).
Courts in South Carolina recognizes four “fault” grounds for divorce:
In addition, there is one “no-fault” ground recognized by South Carolina courts, called “Living Separate and Apart for One Year Without Cohabitation.”
Under South Carolina law, a separation is when the parties live in two separate locations. Living in two separate bedrooms in one house does not qualify, though if you have a separate garage apartment or guest house, that may qualify.
In the absence of the above, you would have to file on grounds of adultery. You don't need direct evidence or a "smoking gun" as evidence. A showing that the accused spouse and the paramour (the person he is cheating with) were disposed to commit adultery and had an opportunity to do so will meet the plaintiff spouse’s initial burden, even absent direct evidence.
Accordingly, adultery may be proven by circumstantial evidence that establishes both a disposition to commit the offense and the opportunity to do so. Hartley v. Hartley, 292 S.C. 245, 246-47, 355 S.E.2d 869, 871 (Ct.App.1987). As one appellate court has noted, “Because adultery, by its very nature, is an activity which takes place in private, it may be proved by circumstantial evidence. Indeed, if it were not for circumstantial evidence, the practice of adultery would scarcely be known to exist.” Prevatte v. Prevatte, 297 S.C. 345, 377 S.E.2d 114, 118 (Ct.App. 1989) (citations omitted; emphasis added).
Generally, “proof must be sufficiently definite to identify the time and place of the offense and the circumstances under which it was committed.” Loftis v. Loftis, 284 S.C. 216, 218, 325 S.E.2d 73, 74 (Ct.App.1985).
Evidence of adultery can include things like romantic cards, love letters, text messages, emails, as well as things like receipts for gifts bought for the paramour, hotel receipts, trip expenses, etc.