Having healthy boundaries in relationships is a huge factor in truly enjoying a friendship.
Boundaries in a relationship would include respecting each others emotional and physical space. We should not feel smothered in a relationship and if you're feeling smothered, you're experience unhealthy boundaries.
Do you get a text or e-mail and feel like you have to respond right away or the person will question why you didn't respond? Do you feel like you can't let a friend know you're doing something or they will be upset they're not invited? Do you avoid a certain friend because you know they're going to ask more of you than what you're able to give? Do you have a friend that is jealous when you spend time with anyone other than you? Do you have a friend that dominated every conversation?
A true friend allows you to have other friends, allows you space, and is sensitive to your personal space. They're not jealous of other friendships and understand there place in your life.
Do you have a friend where your boundaries are very unclear? How do you handle these types of friendship?