Most Helpful Girl
If someone likes to say ironic things and the other takes everything at face value, there is going to be a lot of misunderstanding.
It's the same if one is someone who tries to solve problems by using the "ignore it and it will go away" direction and the other is someone who wants to address the problems to solve them.1
Most Helpful Guy
Unlike popular belief relationships are built on honesty not trust. People will wit Houten a doubt mess up sometimes, that just is how life works. You can't expect them to be perfect so you can't blindly trust them. If you get suspicious it is important for you to _honestly_ express those concerns instead of just brushing it off and saying "I trust him/her" and it is likewise just as important for the other person to _honestly_ address those concerns. Also any time something is wrong with the relationship, you are developing feelings for someone else, you do not feel there is enough communication, y'all aren't hanging out enough, etc. It is vital that you honestly tell them this as soon as possible or it will never get resolved and build into a larger problem later down the road.
I am not saying that you should always be going all crazy-stalker on your significant other or that you shouldn't take them at their word, I am saying that building a relationship around "trust" will cause a lot of things to go on without being addressed because they feel they have to blindly trust their partner.
Not to mention almost every time I've seen a case of someone cheating the perpetrator will constantly say things like "you need to trust me more", "why don't you trust me?", "trust is the most important thing in a relationship so you need to just trust me" instead of answering the question.3