Need some advice please

So for a few weeks now i have been getting a really unpleasant smell in my bikini line and on my vagina flaps. I dont sleep with different men (i have the same sex partner for 5 years) , i do use shower gel on my bikini lines and on-top of my vagina flaps but i NEVER put it inside. Could this be causing my unpleasant smell? It really is a horrible smell, sometimes i can smell it through my leggings or jeans, the odour is strong! I always get paranoid that other people can smell it.

I have also heard if your partner sleeps with someone else it can cause this? Is it true ? My partner did leave me for someone else a few weeks ago but he said they didnt sleep together only went on a few dates but i dont believe him!

What could be causing this please ???