1. Sex Becomes Irrelevant
When your partner seemingly stops caring about sex, that is a big red flag.
A relationship should not get to a point to where either person does not care about intimacy.
Even if there has been no cheating yet, the thought of it will arise.
Never give your partner a reason to cheat physically or emotionally.
Try to initiate sex and romance in your relationship.
Try different things like wearing lingerie, having candle-lit dinners and soft music to help set the mood.
If your partner is getting these things at home, they have less chance of looking for it elsewhere.