Can someone teach you how to be happy in a relationship? Probably not. But you sure can be helped with some necessary pointers. The trick is pretty simple, it just takes a little effort and a whole lotta love. If your partner and you are willing to make it work, then nothing can stand in your way.
Honesty goes a long way in making a relationship happy. From the habits you both disagree on to the genre of music, movies you prefer, never lie your way into being liked by your partner. However, there is a thin line between being honest and being brutally mean. Be sensitive about the remarks you make because at the end of the day this is the person you're in love with.
Do not shun away from confrontations, they help build a closer relationship. No, you don't need to be violent or even swear at each other, if that's not your thing. Even if you respect your partner, fights that turn into arguments or loud discussions are OKAY. But you almost always resolve them as adults holding no grudges and work together towards a better future.
I cannot stress enough on this point. Your partner chooses to be in your life, so treat them like the treasure they are. Do not take them for granted, or just assume that they are available at your disposal. Treat this person as you hope to be treated by someone you dearly love.
One of the huge responsibilities of being in a relationship is that you make decisions mutually, not impromptu ones that end up affecting both of you. And that includes taking up a new job in another state, buying furniture for your house together or even planning weekend gateways.
Communication is most definitely the key. Listen to your partner without judgment, create a safe zone for them and their emotions. A sense of empathy and security in your relationship will help the other person come out of their cocoon, and discuss problems or situations with you effectively.
Give your partner time, but also give them space. It's a tricky balance to maintain but once you get the hang of it, it's easy breezy. This is subjective for each couple, so the best way is to have a conversation with your partner about it (refer to point 5).
You both may have come together as one (as the romantics put it) but you are still two individual people. You cannot be carbon copies of each other so it is important to learn to accept your differences. It may be something as simple as music choices to something as complex as life goals. Either way, reach a common ground which makes both of you happy.
Do not, I repeat, do not ignore the importance of intimacy in your relationship. Sex is a huge part but so is cuddling, balance the amount of intimacy you indulge in. Also, always remember that your alone time with each other is indispensable, so don't just meet in a group with your friend. Maybe plan a Netflix and chill this weekend?
Overthinking is the biggest enemy of love. You need to let some things go, don't ask too many questions, do not analyze everything your partner does or doesn't do. In some cases, ignorance is bliss.
Both of you are mature adults, it is necessary to trust your partner and their decisions. At the risk of offering some candid relationship advice, I can safely say that your partner loves you and has your best interest in mind.