We do live in a very busy time, we always run for success and no surprise that some of us do not have time for proper relationships and are ready for an open time of relationship.
However, I do suggest you to talk with your future partner about borders that you and he may have. We all are different and open relationships can be different too, discuss the lines, borders, before you get hurt.
What is the main rule?
Are you friends with benefits or you don't want to know anything about each other? Are you going to spend time together and support each other or it is just a spending night together? Discuss it before you got into a situation where you need help or support and your partner just runs away.
Discuss the limits.
Is your partner allowed to dare your friends? Do you want to know who is your partner’s new date or not? It should be clear before you find out that your partner is going to marry your best friend.
This is not your last chance.
Some people do think that open form of relationship can save their monogamous relationship. It is not a panacea. It can go wrong any minute. Be prepared for anything. And by the way, statistically, for most couples, it is the end of a marriage.
Be honest and do not play with another's feelings.
If someone likes you but you don't, make it clear for that person before you wake up in one bed.
Do keep in mind that it is your life and nobody can judge you for the decision to be in open relationship, it is only your business. Nevertheless, the discussion will help you to protect yourself in case you have different expectations from that type of relationship.
In case you are not comfortable to talk about such things, probably, open type of relationship isn't for you.