Before you decide to go ahead it is important that you discuss this with your partner. He/she needs to be on board before you start a relationship with someone else.
It is very important to be clear with your partner if both of you would share information regarding your relationship with third parties.
You need to have some ground rules in place. For instance some couples prefer to draw a line which they will not be crossing, whereas in other cases both partners have a mutual understanding of having a sexual relationship outside their own.
An open relationship just cannot work unless and until you communicate with your partner and let her/him know about the extent of your relationship with the other person. Communication is very important in any relationship, but it is even more important in an open relationship where the couple is not fully committed to each other.
Do not hide things about your outside activities after you have promised to share the information. You need to come clean so that your partner knows exactly how deep you are into a relationship with the other person.
Usually, couples tend to be in love with each other and have only sexual feelings for third parties. You need to stick to this rule as this way there will be a meaning to your relationship with your partner.
Do not ignore jealousy, as it will hamper your relationship down the road. Usually people think that jealousy does not come between couples in an open relationship; however, if your partner feels you are talking too much or even spending too much time with a particular person, it may cause jealousy.
When this happens, it is imperative that the couple starts talking and removing any doubts. This is why you need to have some ground rules and limits defined, considering the nature of your relationship.