I am probably going to cause some controversy here, but this is a question that keeps popping into my head so I thought I would throw it out there and discuss it.
The essence of casual dating is the flexibility and freedom that it offers, but it depends on your opinion of what a no-strings relationship is as to how flexible it should be.
To most people, a no-strings relationship is a relationship with no prospect of commitment, which means that the normal rules of relationships also apply and this should include monogamy. Not everybody sees it the same way, so is it ok to date and have a no-strings relationship?
As with most things, this would depend on the boundaries which were put in place when you started the no-strings relationship, you did do that right? A couple of ground rules just to make sure you are both on the same page ensures you both are happy and healthy. If this didn’t happen then it’s not too late to put some in place now.
If you both agree to see other people while having a no-strings relationship then there should be no problem, as long as everyone is aware of what is going on. Keeping your options open is not a problem, keeping secrets is, especially if the new date is a prospect for a long term relationship. It might be that you choose not to tell your new date about the no-strings arrangement and this is fine, if the arrangement comes to an end.
From the point of view of the no-strings relationship, leaving the door open if the new date doesn’t work out is an option. If the sex is great then your friend with benefits might be open to putting things on hold for a short while.
From the perspective of the new date, they are not likely to appreciate the arrangement if they want a full-on relationship. When people are looking for love, it is usual to expect monogamy. They probably won’t appreciate the thought of sharing you with someone else, however, if the no-strings relationship is on hold then there might not be any reason to tell them about it.
At what point does a new relationship become permanent?
Again, everyone has a different perspective on this, some people would say after a certain amount of dates (often 3 or 4) while others say it is when things get physical. Either way, it is usually a good idea to put your no strings relationship on hold before things get serious with your new relationship.
However, you handle this kind of situation, bear in mind that everyone has feelings and these should be considered at all times.