<human>: Can you provide a brief overview of the text?

Hi guys, 
Really struggling with things at the moment, and I really just felt the need to get the perspective of those not close to the situation. I guess I just need to vent..

Essentially, we broke up 3 months ago after 2 and a half years together, living together for the last 7 months of that. To cut a long story short, we had a mixture of trust issues stemming from fidelity issues on his behalf from the beginning of the relationship, which at times caused quite a strain on our relationship. Other than this problem, which we acknowledged was a big one, we were best friends, enjoyed each other's company immensely, had a great sex life and were genuinely happy. 

We mutually broke up, and I've been struggling ever since. It's so hard to watch someone walk out of your life, especially when they were such a big part of it and meant so goddamn much to me. We spent the majority of our free time together when we weren't busy with work, study or friends, and we just click. We were in love. 

I've been missing him so much and have been considering giving it another go with him, if we could agree to work through our issues together. But I've just found out he's seeing another girl now and it's hit me like a ton of bricks. I understand if he wants to move on and see other people, but fuck. It hurts.

Basically, how do I deal with this? The thought of him with someone else, most importantly on an emotion level, makes me almost physically sick.
<bot>: boyfriend of 2.5 years and I broke up 3 months ago. Considered giving it another shot. Found out he's seeing someone else. Feels. How do I cope?