If you've never been in a relationship before than it's no surprise that you wouldn't know what to do. But don't panic, being in romantic relationships can be very rewarding and you might actually enjoy it compared to dating and one night stands. However like everything else in life even the best couples have relationship problems.
The way to enjoy a relationship is to try to avoid as many of these problems as possible. You also have to be willing to work things out in order to salvage your relationship. Don't just decide that things are not working out at the first sign of trouble.
As I said before, romantic relationships between two people can work but you both have to put effort into making it work. The first thing to remember is that when you are in a relationship, it involves two people. So the most important thing you need to do in a relationship is to compromise. Learn that you can't always have your way and know when to put your foot down. Giving and taking is part of life and is crucial to keeping a relationship successful. As a man it is vital that you figure out when you need to give. Over giving is a turn off because women will start to view you as a pushover. So just like dating, remember to be nice but not too nice.
Women also love men who are thoughtful so dinner arrangements, surprising her with dates and romantic gifts also help keep the romantic relationship afloat. It'll keep the romance alive and it'll also prevent you from taking her for granted. Just remember that you can't do this too often or she will come to expect it. Worse she will assume that you've done something wrong and you would have created problems for yourself when nothing was wrong with your relationship in the first place.
The next part of maintaining romantic relationships comes from communicating with your partner. You have to understand that women and men communicate differently. A lot of relationship problems actually occur because of simple misunderstandings when the couples are unable to communicate with one another. Take the time to understand your partner and how she is feeling (especially when she is emotional and needs time to calm down). I'm not saying that you need to take the emotional rubbish that women dish out but you have to try to understand where she is coming from and deal with it appropriately and not just slam the door on your way out.
Of course the biggest relationship problems are caused by jealousy and betrayal. It would help greatly if neither your or your girlfriend are cheating types of course. As for jealousy if your girlfriend is the jealous type, either dump her if you can't deal with that, or work out an arrangement with her. Get her to understand that woman A is just a close friend or colleague and nothing more. If you have jealousy issues you might want to meet up with her guy friend and who knows and you could be best of friends. But if that doesn't work out, the best way to deal with it is to try to get over the jealousy issue because if you continue to harp at it your relationship will fail and that guy would have won.
All relationships go through bad times and rough patches. This is normal and the only way for you to ensure that you can maintain your relationship is to avoid as many of them as you can. You also need to keep the good memories in mind and avoid giving up on your relationship on the first obstacle that you meet.