Hi,
I also know exactly how you feel..
I can turn into someone I really do not like when I am feeling jealous - it is horrible, it is a feeling that comes over you, gets in your head and pickles your brain.
I have been with my partner for over 2 years and I believe that he truly loves me.. I went though (and still do) a stage of deeply hating his ex, looking at him and imagining them together, imagining what they did together, the things they said, the places they went... It can drive you insane...
I have learnt that it is such a waste of energy...
It is an evil emotion.
Believe me you have to try and control it otherwise you will push him away - for good.. !
Just think about why you are feeling like this - are you insecure? If so, so things to make you feel better about yourself - go for a run, got to the gym, do yourself up and look at yourself and be happy with what you see..
If you didn't care then you wouldn't be jealous, but you have to keep it to yourself..x