It's a tough thing to battle and an even harder thing to justify.
I never felt much jealousy in my life of other people but I often felt jealous of my friends when they got recognition for something exemplary they did when something I did was not acknowledged. Often theirs was the superior work but I still felt a pang of what must have been jealousy. I often made do with what I had, just accepted that other people were better at some things different from myself or I found a way to better myself to their level, with or without their help. Friends were somewhat easier to get over when it came to jealousy. I was more annoyed when they rubbed it in my face too much, or kept poking me until I snapped at them and may have appeared more jealous than I actually was. In any case, I am rarely jealous of my friends at this point. I actively encourage what they do best and enjoy their talents as much as I can.
Jealousy when it comes to a partner of mine is more difficult. They are more likely to be hit on, to get the glance of other people and certainly to be acknowledged more often for what they do. I find other people glancing at my partner to be somewhat flattering, especially in shopping markets and whatnot. I usually tell them that they were being checked out and by whom for our entertainment! Being acknowledged after my partner or being ignored is OK with me - I live my life in the shadow of other people but I am comfortable with this. I am very uncomfortable being the centre of attention but am quite happy to approach people when it suits me. If my partner is talking to someone they know from way back or such I usually defer to them and try and avoid standing their awkwardly but instead smile and agree with what they say when they say it - it looks better for the person they are talking to and perhaps we introduce ourselves.
When my partner gets hit on it can be difficult. I am more comfortable with people I don't know at all or even close friends doing it - I trust my partner with everyone! It is the people I often don't trust. Some I know the character of and can relax while others can contain supreme flirts and the odd chancer. These make me uncomfortable; not because my partner may give in or anything but rather that the chancer will try something and I won't know what to do. It's difficult but I trust that my partner will handle them - I just have to endure a few moments of stress!
As a rule, I cannot be jealous of exes. They are an ex for a reason; no need to fear them until something happens and even then I wouldn't react too strongly, unless it kept going on, in the which case I would have to conclude the relationship. I hate that word, it's something we only really started using since Facebook! Back on topic; the moral high ground will rise beneath you in the case of your partner cheating on you with anyone else; especially an ex! If my partner was constantly talking to their ex and texting and all sorts, I wouldn't be perturbed or I would try very hard not to be. I might confront them about it, but in such a way where they would explain what was really going on and I wouldn't seem suspicious or accusatory.