Hi LostBirdie,
Welcome to SR, you are in the right place and I think you find a lot of information to help you understand your ex and what was going on.
My ex and I broke up a few months ago after 11 years together and the last 6 of those were his addiction progressively getting worse and I couldn't seem to walk away. I applaud you for walking away (even if you didn't technically do the breaking up). I encourage you to focus on you and allow yourself to grieve. It took me months to start feeling better, but because I really grieved and allowed myself to hurt and cry and feel desperate and alone and all the horribly sad feelings of letting go of someone I loved dearly and all the dreams I had for us, today I feel happy and strong. I know you are in a lot of pain, but I promise you it will get better and you will feel better one day. I found it is in these moments of pain that I would talk myself into going back, minimizing the addiction and believing he would get better - all the times he told me he would.
I hope you can keep your strength when I could not.
One thing I want to address, you said
My story may not as heartbreaking as the stories I have read in these forums, and to be honest, I don't even know if it would be classified as an addiction or a user, since he would do it once a month, but incrasinly to every 3 weeks in the last 3 months
To me his behavior absolutely qualifies as addiction, please don't be in denial about that. What he is admitting to is probably a small fraction of what he is actually doing. Your story might not be as bad as what you read on here, but it will get there, the disease is progressive and only gets worse unless he stops forever and embraces real, lifetime recovery - not just sobriety. Trust me, you do not want to continue on the journey of addiction, it is ugly and will take both of you to places you can't even imagine.
I wish you the best during the painful time - sending you strength and love.
xoxo