While there could be an underlining reason for her lack of interest in sex right now and to why she feels that you may need more sex than she does or will in the future - I have to say that some couples (partners) are ok with there being a third party in the relationship as long as they are your main love and the source of your emotional bonding.

I personally do not see how a relationship can survive in the long run with a third party being involved, but then again thats me... my husband feels the same way.