Worried that fiance will be lured back to his ex-wife again

I'VE been with my fiance for three years but it hasn't been plain sailing, as he has an ex-wife and two children.

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The stress of it all got a bit much about a year into our relationship and we broke up for a bit.

We missed each other and decided to give things another go and now were very happy.

The problem is when we split up he went back to his ex and they slept together for a while before realising it was never going to work.

I found it very hard to get over the fact he slept with his ex because it felt like our relationship had meant nothing to him. I also think it was a bit of a victory for her and that she holds it over me.