Agreeing to an imaginary "contract" with your significant other is always a little nerve wracking, that's why trust is a huge percentage of the transaction. Without trust in yourself and in your partner, your relationship is doomed. The imaginary contract is pretty much common sense: respect, no lies, no cheating and just be there for one another. That's pretty basic although sometimes things can get a little tangled, confusing or misinterpreted and we start looking into things to "protect" our relationship, or so we think we are protecting it.
It's really important to learn how to read situations and know which ones are a threat to you or not, although you have no control over your partner and that is important to understand.
What you have control over is YOU! what you have to offer and the life you create for the both of you. This is what I mean by knowing your worth, If someone wants to be with you, there are a million reasons why they made the commitment and some are unexplainable because it's a subconscious factor that links you to many different aspects that makes him feel alive when he's with you: Your scent, your aura, your voice, your skin. Basically, it's you and that's it.
With that said, there's no point in being the police with your other half because bottom line, if he or she wants to ruin things, the life you have, everything that is offered and given with love...well it's really on them. Yes, it hurts and yes you will survive. Just know you worth by being the best you can be for your partner and wish them to find someone like you again if they ever decide to cross the line. Life works in mysterious ways and there's no going around that, Karma is also a pretty sweet devious baby and the truth always comes out, no matter how hidden it wants to be.
Don't waste your time in looking for things that can go wrong or people that can come between the two of you. If you are in a hurtful situation, communication is the way to go but be careful to not create that situation yourself. If you truly trust your other half, you should own the serenity that they will not hurt you. Nothing and no one is more of a threat than yourself. It's not the easiest advice to go by but it does eliminate a lot of stress and anxiety.