Asking for a friend: ‘I’ve been sleeping with my ex but being friends with benefits is just making me feel lonelier’

Q: I broke up with an ex a year ago as the relationship just wasn’t really going anywhere, and I felt we were growing apart. It didn’t end badly, and we still see each other from time to time as we have mutual friends. I have bumped into him more than usual recently, and we hooked up a couple of times. I was thinking that we could be friends with benefits or something casual, and he seems to feel that way too, but something doesn’t feel right. The sex is fine, but it is just missing something. He stays over sometimes but leaves early, and we don’t really chat too much when we don’t see each other. I’ve been single since I broke up with him and I am very lonely a lot. I do go out but haven’t fancied anyone in ages, so I guess my ex fills a gap for now. Sometimes I feel lonelier after being with him, especially if he leaves in the middle of the night. Why do I feel so confused? I thought friends with benefits would be easy, but I’m not sure now. Am I just going to be lonely forever?