I guess it would matter what exactly about this person triggers you. If it is something like how they walk, talk, breathe, eat.....that's not going to change....so maybe spending less time with them is the way to go.
If it's a personality issue, again, more than likely it's not something that is going to change unless they want to make the change (and it takes a long time at that).
If it's a habit of popping their gum, cracking their knuckles, picking their nose, well those things can be halted or changed fairly quickly and maybe talking to them would be beneficial in getting them to stop while around you.
Is it possible to be with this person when there are others around so that your attention is not strictly on this individual? If so, it might be easier to deal with whatever they do that triggers you if you have distractions from them during your time together.

sabby