Friendships are important in establishing an identity outside of a serious relationship. Men sometimes have a hard time doing this, which could explain why they are often more heartbroken after a relationship ends than women are, according to a June 2010 study published in the Journal of Health and Social Behavior and reported on by Time.com. One reason for this might be because women usually have more friendships and often form strong emotional attachments to their female friends. Such friendships allow you to share hobbies and outings that perhaps don't interest your significant other, and your single friends can become a support system in the event that your serious relationship ends.

If you find yourself wanting to spend more and more time with your single friend, tread cautiously: The friendship could lead to an emotional or physical affair if you aren't careful. Researchers at the University of Wisconsin-Eau Claire found that the majority of committed men and women who had opposite-sex friendships admitted to being at least a little attracted to their friend. Although the study focused on heterosexual men and women, it's not a stretch to think the same attraction happens among gay and lesbian couples and friendships. Take some steps to make sure the relationship you have with your single friend stays purely platonic. When you meet him, meet him during the day, in public places. Keep space between you physically. Finally, pay close attention to your intuition. If you suspect your single friend has feelings for you, and you value your romantic relationship, stop spending time with your friend. It might hurt both of you, but it will probably hurt a lot less than a breakup would.

It's not just attraction between friends that can cause friction in a serious relationship, either. You may not be attracted to your best friend, but that doesn't mean you don't want to spend a lot of time with her. You might even be a bit envious of her single life. Because of this, your partner may not like it when you spend a lot of time with your single best friend. He might think she will be a bad influence on you. Reassure him that this is not the case, and make sure your single friend understands that your romantic relationship is important to you and that you won't be hanging out at the singles bar with her anymore. She may be upset, but hopefully she will understand. The fact of the matter is that friendships change when one friend becomes part of a serious romantic relationship. A true best friend won't mind making a few sacrifices because of it.

It's important to determine what your significant other is comfortable with when it comes to cultivating friendships outside the relationship -- especially if those friendships are with people who are single. Friction can occur when you start spending more time with your single friends than with your partner, or when you choose spending time with your friends over spending time him. This can cause resentment, so it's important to manage the time you spend with your single friends wisely. As a couple, you need to have a serious talk about how you feel about each of your friendships, then you need to respect the boundaries you set for each other -- as long as they are within reason. If your significant other becomes too controlling, such as forbidding you to see your friend or reading all of your texts and emails, you may have to decide whether you want to be with him at all.