Hi Natasha,

If you are not in love with him and not interested in him anymore then it sounds like you might have to make the move and go your separate ways. If this is the case now, it is unlikely that you will have feelings of being in love with him again. It sounds like him messaging the other girls has confirmed the decision in your mind. But if these feelings were there before you found this out then try not to use it as an excuse or justification for what has happened. You might find yourself being talked back into something you don't want.

If you still want to be friends, then try to be as sensitive to his feelings as possible. If you have felt a distance, chances are he has too. If he was messaging other girls then this could be a sign that he is also ready to move on. It might not be as out of the blue as you expect.

You have touched upon some good things to perhaps say already- that you still love him as a friend and that you have a great time together. If you dwell on the negatives about not being interested in him anymore and having less sex, it is human nature to take these things away rather than the fact that you are better off in a platonic relationship, so he will probably feel deflated.  

It is probably doing him more harm by staying with him and letting him think things are fine when they are not. He might drift apart from you for a while, as break ups are often times to reflect, however if you both love each other enough you should make the effort to get back as much of the friendship that you had.