I am a gay man and have been in a relationship for several years with my partner, but we struggle sexually due to my lack of sexual attraction. I try to satisfy my partner regularly, but often fantasise about other men being involved or my partner having sex with other men. I love my partner wholeheartedly and he is extremely attractive, amazingly attentive and understanding, but I find that, as soon as someone has become familiar, I lose sexual interest. Once I have “completed a conquest”, I want to move on. It creates tension in our relationship, as he feels undesired by me, which, in most respects, is not true. I fear it is related to the struggle I had when I was growing up to accept that I was gay – something I am long past. Maybe I just like being a cuckold. Can you help me to accept my sexual desire for my partner and give him the love he truly deserves? It is not unusual to have powerful fantasies that appear to threaten a relationship. The very forbidden nature of them makes them more exciting. Your fantasies are yours alone: you can choose when to indulge in them and when to set them aside; you can choose whether to share them with another person or to keep them to yourself. You seem to be afraid that you may not always have choices when it comes to acting them out or not, but you do. You can choose to make a fantasy real and potentially destroy your relationship, or you can relax and be at peace with your thrilling mind-erotica – and even use it to enhance your sex life with your partner. Your choice. Pamela Stephenson Connolly is a US-based psychotherapist who specialises in treating sexual disorders. If you would like advice from Pamela on sexual matters, send us a brief description of your concerns to private.lives@theguardian.com (please don’t send attachments). Submissions are subject to our terms and conditions: see gu.com/letters-terms. Comments on this piece are premoderated to ensure discussion remains on topics raised by the writer. Please be aware there may be a short delay in comments appearing on the site.