Just to clarify, my previous post was not meant as a full answer I was pausing to wait for your to read what I had written so far and then respond with further questions, etc. This can be an ongoing conversation and I won't attempt finalize my answer until your are happy that I have answered any & all questions you have.
So, the dilemma faced in this situation is that obsessions within the context of OCD is very much focused around uncertainty - questions or possibilities that it is very hard to ever be sure about. This is the nature of the disorder and makes the provision of reassurance nearly always futile. Individuals suffering from OCD become obsessed about the possibility of something and feel driven to seek certainty - which is usually possible to obtain.
For example, ritualistic checking is a very common OCD symptom. In this situation people repetitively check things like door locks, light switches, etc because they become obsessed with the possibility that the item may be unlocked/switched off etc. The only way they can seek assurance is to keep checking but this immediately fails as soon as they walk away (and need to check again).
In similar fashion individuals who become obsessed about sexual identify become obsessed with the possibility that they are (for example) gay and become disturbed by any thought, image, situation or behavior that could possibly suggest they are gay. Reassurance usually provides some relief for a brief period if at all) before the anxiety around the uncertainty becomes intense and they need to seek further reassurance.
The botXXXXX XXXXXne for all of this is that even if he is desperately seeking reassurance providing it won't help as it just feeds into the cycle of obsession and ritual. There are well know and effective treatments for OCD and I would be happy to discuss these with you if you would like.
I will pause again here and wait for your response to what I have written. Please remember that I am not intending this as my full answer yet, I am just giving you the opportunity to respond at this point in time. You don't need to request a re list due to incomplete information, just reply to this thread.