First, let's give credit where credit is due. Shane did try to get Rick out, so there is no doubt there was a genuine friendship in there. And there is nothing wrong with two people finding comfort in each other after being united through loss. But getting involved with your supposedly dead friend's wife requires a little finesse. This means not jumping in the sack at the soonest possible moment. A mere couple months had passed between the outbreak and Rick's return, which seems like an unusually short time period to go from mourning to boinking, especially given all the commotion. Rick's return demonstrates exactly why this wasn't wise. After that point the foundation of the relationship between Shane and Rick was changed. Despite this there was still a chance that things could have remained positive and civil between them had Shane acted like a rational adult, but he ended up handling the situation poorly. The real screw up on Shane's part was his inability to let go. Once Rick showed up any dreams of being the new patriarch of the Grimes family should have died. Yet Shane kept that dream alive to the point where it confused him and turned him against his best friend. And that's just plain stupid and petty. But Shane's dumbest decision was still to come.
