NEVER EVER marry someone who is not interested in sex!!!
Check out a group here called 'I live in a sexless marriage". It will give you a REALLY GOOD preview of coming attractions. The reason doesn't matter but odds are she has little to no libido. It could be that once the relatio0nship is settled she looses interest. That would explain the multiple partners. She lost interest in them as well. So don't take it personally. But whatever the reason this makes her a BAD match for you. Thank your lucky stars you found this out BEFORE marriage. Many men AND women get the bait & switch pulled on them. Then it is too late.<br />
Best of Luck<br />
No matter her reasons or excuse, its only all forms of bad. If she's either with someone else, or has lost interest in you, or in sex in general (unless its medical), you have got to let this one go. Imagine never having sex with her again in you life if you stayed with her. Could you do that? Would you cheat to finally get laid? Hard questions, but best dealt with now, trust me.
For whatever reason, she just doesn't love you anymore. You probably still love her, but that's just not the point. There is no point, and much pain in loving someone who just doesn't love you back. You have different sex drives, or different roadmaps. Lucky she is not your wife. I have empathy because I am going through excactly the same situation. Hurts like hell, especially if you once did enjoy a great sex life, but now it's just not on the table anymore...You have to let go. The sooner the better. Do not invest any more emotional energy on this "sinking boat"
Her hormones could be affecting her sex drive. Or it's very possible that you didn't satisfy her sexually. Whatever the underlying cause, it might be time to go your separate ways.
You and her do not have chemistry,time to find someone new.Thank her for letting you know early on.No point in trying to find new ways of turning her on,you are wasting your time.Move on.
I'll second TM's reply. Run like hell, don't look back. Find someone who love's sex and is a giver. Trust me, I've been married 16 years and almost never have sex with my wife. She says it's just not that important and has other, better things to do with her time, or is too tired. Find someone else.
She's lost interest in you or she's got comfortable and no longer thinks she has to bother and the less she bothers the more effort you put in. Find someone else.
It appears to me that she may have found someone else and is using that as an excuse.