I think it's so important to surround yourself with people who support the health of your relationship with your partner; that you have healthy men and women who are in integrity around you and will not dishonor your relationship under any circumstances. And that you, yourself, as someone who is supposed to love, honor, respect and protect what you are building with your partner, are always in integrity.
The lines can often get blurred when you do not put boundaries in place and allow men or women to come into your relationship, possibly with ulterior motives. If you are in a relationship, it is wise that whomever you are friends with knows that you are in a committed relationship and it is your responsibility to out the necessary boundaries in place to ensure there are no blurred lines.
If you have friends, your partner should know about them and your friends should know about your partner. If you have to hide your friendships from your partner that is a clear indication that you are operating outside of integrity and your relationship may be headed down a dangerous road. If you have friends who are now honoring the boundaries within your relationship, it's either because you haven't set clear boundaries OR they are choosing to dishonor the boundaries which means they are dishonoring you as well as your relationship.
When you choose to surround yourself with married/partnered friends who are in healthy, loving relationships, not only are you able to experience examples of what it looks like to be in a healthy, loving and integral relationship but you are if possible, your partnered/married friends can hold you accountable, let you know when/if your perspective may be distorted around different relationship dilemmas that may arise between you and your partner while supporting your relationship and assisting in getting you back on track.
Relationships are a beautiful blessing and it is my belief that if you truly desire a healthy, sustainable relationship, it is wise that you take great care with your actions in making sure that you protect what you've been blessed with.