Normally rebound relationships don't last 2.5 years... but if it was, it makes sense that you are even in more pain now. Because a rebound relationship is a situation you get in to avoid the pain of a breakup. So you never experienced the pain of the first breakup. And it has been festering for 2.5 years now. So it is going to hurt.
And while you say your relationship was a rebound, it lasted for 2.5 years, so you must have developed some feelings for this guy in that time period. So you are also hurting from the end of that relationship.
So, to do the math -- (you are in pain from your last relationship of 2.5 years) + (you are in pain from your previous relationship) x (the time the pain was left unattended) = a buttload of pain. Just take deep breaths and understand that it will get better. Take a little bit of time for yourself. And whatever you do, don't jump into another rebound relationship.
Good luck.
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