Are you in an open relationship or are you monogamous on your end? Your partner sounds dishonest, immature and seems to want to rekindle things with his ex. There are red flags everywhere, from him jerking to ex hookups to keeping in contact with people he has "no friendship with" and being dishonest about it. I would suggest couples counseling but to be frank, I don't think it would help much since your partner clearly has a lot of growing up to do which is often the problem in younger/older relationships.

Personally I would have a frank talk with him and say it seems you and he are at two different stages in your life, he is still stuck on his ex and wants hookups and I assume you want a serious stable committed relationship. If he makes a serious effort to reform and recommits to you and the relationship, see where it goes but I honestly don't think it will last more than a few months before issues start coming up again. If things work out, great, if not, consider this a learning experience and keep an eye out for red flags in your next relationship. I would suggest trying to find someone more mature who is looking for the same things you are and appreciates you. It's never fun to be in a relationship when you are in the position pursuing the other person and they don't esteem you to the same degree.