Why did my lips bruise from a mild kiss 3 months of having lip filler? (Photos)

The lips are quite vascular.  During injections, small, yet deep bruising may occur in the obicularis oris, which is the lip muscle.  The bruises tend to organize over 6-12 weeks, and then can move to the surface through the muscle with mild stimulation.  This could occur while you were eating as well, so it was not the kiss.  This should resolve quite quickly, and bromelain and arnica may be helpful in shortening the length of time that the bruise is present for.