He's going back to his ex, but I still want him - can I do anything at this time?

So, I started a new job nearly a year ago, & within the first day it was like I had known this guy my whole life. We clicked on everything.
He had a girlfriend & I had a boyfriend. So never gave it any thought. Then I split up with my boyfriend but still didn't give it any thought.
Over a few weeks it became apparent that we had strong feelings for each other. On a night out we got together. We didn't have sex. He was still with his girlfriend. We saw each other again & it was obvious the feelings ran deeper than being purely sexual. A week later he tells me he's left her because he wants me. We had a perfect (if short) time together then I went away 1 weekend & he told me he wanted to go back to his ex. I was devastated. But let him go. A few days later when I returned to work he told he'd made a mistake. We tried again. Then he told me he wanted his ex back. Then he came back & told me he loved me & I was everything he wanted. Tried again. After he told his ex he was moving on, she contacts him & says she wants him back. He's left me again. I've let him go back to her. All this has happened in 4 weeks. Him & I share a lot of common interests & we honestly have an amazing connection. His ex & him... well apparently she doesn't like to do anything he does. I don't know about their relationship or anything else. Just that he's not over her & says he needs time and he's confused. I think he knows what he wants tbh. I now know he's a liar, & a cheat obviously. I know I shouldn't have got with him that 1st night. Sadly I have never seen a future with anyone before & I really do see a future between us. Which would work if he was obviously over his ex. Other than letting him get on with it, is there anything I can do about this? I still work with him which is both an advantage & a massive disadvantage. I know I should bin him off. I've read back what I've written and it's slapping me in the face with the answer, but I'm not ready to stop fighting for what I believe in yet.
He's going back to his ex, but I still want him - can I do anything at this time?
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