Thanks for your question.
Unfortunately there isn't going to be an easy way to get over such a long relationship, and it may take some time. However it sounds like there were some pretty big problems in your relationship as well including the lack of trust and him being unable to create some healthy boundaries with his mother. These are problems that would need to be solved in order for your relationship to work out in the long run, and sometimes it does take some time and space for people to figure those things out before they are ready to give a relationship another try.
It does sound like he is handling the breakup in a completely different way than you are, and I can understand that you don't want to be plan B. Some people handle breakups by trying to distract themselves with other people, others want to be alone like yourself. So I wouldn't assume that just because he is trying to date and see what's out there, that he is necessarily moving on, however that does seem like something you may have to prepare for.
In the short term it is going to be painful. While there may not be a lot of things you can do to make this easy, there are some things you could do to make it less difficult. Checking his email is likely going to make this much harder, and prevent you from moving forward. Because of that, one of the best things you can do for yourself right now is to avoid looking at this email and anything else that could feed into some of this depression that you're going through. It is important that you are taking care of yourself, and not being afraid to reach out and talk to people if you are having trouble. Getting over a 6 year relationship is not easy, but once you do start to give yourself some space from it all, each day will start to get a little easier.
I definitely wish you the best with all of this, and if there's anything else I can do to help please let me know.