Hi Alec,

That all depends if you want an open relationship with your girlfriend or not. If you are happy for her to sleep with other men as well as with you then that is up to you as a couple and what you feel fits best for your set up.

The fact that you have used the word ‘cheated’ suggests that you didn’t have that type of relationship with her- that perhaps you assumed that she would be monogamous. How do you feel knowing that she cheated on you and that she is using his penis size as an excuse to go back to him?

If you are comfortable knowing that she is potentially getting more satisfaction from this guy than with you then you need to be very comfortable in your own skin to pursue an open relationship with her. If you still have an active and fulfilled sex life together then this could work between you both.

That said, an open relationship is generally agreed upon by both sides of the couple and does not usually materialise after one person has cheated on the other.

If you want faithfulness and she is already thinking of going back to this man, then it sounds like this is something that she won’t be able to maintain in future. If you think you could cope in an open relationship then this is also an option for you but be mindful that what you are feeling right now, you might feel every time you know she is going to see someone else. Protect yourself from getting hurt by making the decision based on what your know about yourself and what you want from a relationship.