I'm sorry you are sad, and missing him. I do think it is a part of dating and relationships. When you do let someone in beyond a superficial level, it's pretty normal to miss them and grieve for them. You with your ex since you were kids. This seems to be your first dating/adult relationship since the D and as an adult. So, it's going to sting a bit and maybe a little longer. Don't let this hold you back from letting anyone else in a again. I think sometimes we just need to be aware this a normal part of the process, even if it stinks.