The answer would be love. Without love there is no relationship. That is true. But apart from love what else is required in a relationship? 

1.Respect: Without respect for your partner's needs, emotions, feelings, and most importantly without any respect for your partner's past, love alone cannot support the entire relationship. Every human being is full of emotions, those emotions may not resonate with yours but that doesn't mean those emotions don't need validation. Being a respectful partner would add joy to your relationship.

2.Communication: Communication is a must. People don't have the superpower of reading minds yet. Don't expect your partner to read your mind. Tell him/her what's going on with you. It is where you make a bond. A connection forever. Also, listen to what your partner is saying. Not everything is about you. There are two people in a relationship and both are equally important.

3.Trust: Trust is one of the main components required for a healthy, long-lasting relationship. What's the point in committing to someone one doesn't even trust? Today's times are hard. One might have to talk to many people about business-related issues or anything and that might be scary for our partners but it is important for our partners to have trust in us and also it's our responsibility to maintain that trust. 

4.Friendship: Be friends with your partners first. Friendship is the foundation of every healthy relationship in the world. Friendship adds fun, understanding, that's why we also hear “marry your best friend”. Or you can make your partner your best friend. As simple as that.

Life is easy but we intend on making it complicated. Tell often the people around you that you love them. Be thankful! Be grateful for what you have. Tomorrow is not promised. Ego isn't anybody's friend. Know your worth. Apologize where it is required. Grow, learn and speak out what you feel. Help in making someone's day awesome. Don't let anyone belittle you. Be there for each other. Discuss a problem, try to solve it, and try not to repeat it afterwards. You might be here today but there will be a time when you'll have to leave it all behind. So give people happy memories to remember you by, stop making things difficult for your ownself. Keep it simple, and put effort into what you want.