How long ago did you break up? You also seem to still be rather emotionally intimate with him, given than you are still communicating with him and he confided in you that he visited a sex worker. It's difficult to move on from a romantic relationship if that person is still a part of your life. I am friends with most of my exes, but there needs to be some time passing to get over each other before you get close as friends.

I think it's normal to not be able to imagine being with other people - especially since he was your first sexual partner. Everyone is different. I think it's good that you're being gentle with yourself and not trying to rush moving on. Getting over a breakup can be a slow process. After my last breakup, even though I have been in many relationships, it was difficult for me to imagine wanting to be sexual with someone new. It took about a year for me to not feel that way. It was a big love and a tough breakup so opening up that part of myself to someone new wasn't something that was easy to imagine when I was still in pain. Give yourself time to heal.