Back with another girl?

My ex boyfriend and I broke up 2 months ago. We were together for 1 year. he's now back with his old crush.
We were friends before at university and I liked him as he was really attractive but he was not into me.
We began dating unexpectedly and I was a bit surprised as to how he was showing interest in me.
Considering I was the only source of help and contact he had during this time for certain reasons.

We were in LDR but he returned to London just a few months before we broke up.
Our relationship was not bad and it was good. We were both sexual people so we both loved sex and there was a lot of going out, hiking etc. He even met my family. Everything seemed okay but we did have several arguments and he was really stubborn. So was I and at times we had fights which resulted in both of us giving each other the silent treatment. Eventually, he would cheer me up but this was there.

I felt I was the only girl my ex was seriously dating until I found out about his new girlfriend. I have seen this girl before and have briefly spoken to her at university. What I didn't know was how she was his "love". Only after, our relationship broke off, he crawled back to her and he told his best guy friend whom I'm also friends with that our relationship taught him how she was ALWAYS the ONE and how our relationship made him realise how much he missed and wanted her back.

Apparently they never had a relationship because of his attitudinal problems but he forever regretted that. He was also "in love with her" since he met her and could never get rid of the unresolved feelings for her. He was also saying that she was his physical preference type of female. He had moved on from her rather quickly and started dating me but claimed I just made him miss her even more.
Now he's with her and he looks super happy.

I dont get it. How can a relationship teach him her value?
Back with another girl?
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