Does your partner have a wandering eye, and ogle other people while with you?
First, it is natural for humans to appreciate beauty in all forms. Just as you might look at a gorgeous sunset, or a beautiful beach, you can appreciate the beauty of a well-formed man or woman.
The question is whether your partner appreciates your unique qualities more than that person, and if he/she shows this appreciation. If your mate is always staring at other people, but rarely compliments you on your own qualities, it is time to remedy this. Sit down and talk about why this happens.
If your partner neglects you in favour of spending time with others, it is time to talk with him/her. A partner should respect the mate over others, and if the choice is a lonely mate or a "fun" friend, the mate should come first.
If you are feeling neglected or overlooked, sit down and talk about this with your partner. Look through the jealousy tips - you need to be realistic about how needy you are, but you also need your partner to respect you.