New sex partner - help?

I'd been in a relationship with this guy for about a year and for the last six months we've been having sex, great and a lot of sex. but under some circumstances, it had to come to an end. I've only had sex with one other person before. My problem is I've become so comfortable and used to this person, emotionally, mentally and sexually, It seems I'll never be able to be comfortable enough to have sex with another person. Like I can't even imagine, literally imagine, physically being with anyone else. The person just made me feel so amazing and more importantly incredibly comfortable because we had a great "relationship" and everything was just easy going. It's so weird to even talk to other guys let alone think of them sexually, and I don't want to have this feeling but I can't break myself from it. I feel like I'll always be stuck on him, who I won't be going back to. *sad face emoji*

You have put it on paper that it's come to an end and so it's ended. Your feelings and emotions about this are normal. We all take time to get over intense relationships which come to an end. Time helps us and WITH time we come to realise and learn from past situations good and bad. You need to step back and understand that if your relationship was meant to continue, it still would be. There's a reason for it's ending, regardless of the circumstances that you know. Time will enable you to find this real reason.