Move on dude. It sounds like the relationship did work for a reason. Sounds like you got jealous cause you think she is the best you can do. My advice, cut it off completely and go out and date A LOT. You can't depend on anyone, but God to make you happy. She won't, because she is human and imperfect. I encourage you to man up and realize that maybe there is a more grounded, beautiful, and mature women out there. If she is seeing another guy, then you should go see another girl. And not just to make her jealous. You will find love again, but a inter-dependent love that does rely on another person to survive. I used to sound like you, now I realized that there are a lot of great girls out there. I can't stand it when people say, "one day you'll find that ONE special girl." Get that out of your head, you can have a healthy relationship with many women out there. Right now girls out number the guys on Earth, so stop worrying about one girl. Trust me... she is not that special. You just think she is because perhaps you've been viewing relationship incorrectly.
If I told you that you and I were going to be locked into a warehouse for 5 days, with 100 people, and we only get 5 bananas each to sustain us for those 5 days... would you share? (no) Because everyone got 5 each, and I will need it to be sustained for being locked in for 5 days.
Now, what if just me and you were locked into a warehouse for 2 days, and we had 6,000 bananas each. Would you care if I took one? No, right (of course not) This is what my world is like. Their are millions of women on this Earth, and I'm not going to get sad and lonely over one.
God created you to be a man, so start acting like it. Start being the man you want, and not the one you think everyone says you should be. What women say they want is not want they respond too. Good luck man.