Finding out I was bi-sexual by cheating on my first boyfriend with another girl

Just got done writing this and realised how long it is. Got a bit too carried away with the back story and all the little details as I’ve never done something like this before but it really turned me on reliving the experience. TL;DR My (ex)boyfriend stood me up a few times in a row after I’d moved to uni. On a drunken night out my good friend at the time took me back to our accommodation to comfort me and we ending up fucking for most of the night.

It happened during my first few weeks at uni. I was 18 at the time and was with a guy a few years older than me (we’ll call him Jack). Jack and I had been together for around 3 years, and looking back it was obvious he wasn’t too into me at the end of our relationship, and would only really see me if he knew there was sex involved. But at the time I couldn’t see it, I thought I loved him more than anything, and was kinda star struck by him as he was an older, popular guy who was very handsome. He made me feel lucky to be with him and that lead to him being able to get away with treating me badly.