I think that the key to a good relationship is to trust each other.
To trust doesn’t mean telling your partner everything. It means just trusting them and not getting suspicious. It’s normal to have a pinch of jealousy. It doesn’t hurt the couple. When two people grow with these two ingredients, they will get along for the rest of their lives. Each one has to look after the other. Rather than the existance of me and you, it should be we. I know someone who spies on his partner's phone without cause. This is wrong. If you catch your partner doing this, it will be a mess. It’s an unpleasant situation, especially if you have children. The couple must focus on healthy actions that are useful to them.