Keikenchi Chochiku de Nonbiri Shoushin Ryokou: Yuusha to Koibito ni Tsuihou sareta Senshi no Mujikaku Zamaa

After losing his girlfriend to a brave hero, Tooru is expelled from his S-Rank party. With a feeling of sadness and pain in his heart, he defeats a demon he meets outside the city, and his ability "Saving Experience" is broken! Tooru becomes level 300 in the blink of an eye!

(Source: Kadokawa, translated)