Why is he using Tinder?

I saw a guy I know on Tinder, he is in a international relationship with someone that lives on another continent and has just arrived home alone on Thursday after spending 8 weeks in her home country. I know he used it recently and not forgot to delete it as he has uploaded pictures from his time in that country. I'm surprised to see him on Tinder as they both post pictures of them and seem very in love. Should I tell his girlfriend? Why is he using Tinder?
Why is he using Tinder?
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