Should I excuse his hookup behavior since we aren’t technically dating? Or is it a red flag?

Anonymous
I moved for a study abroad internship for half a year. Prior to moving I dated this dude casually for a few months but since I was moving away we kept it casual. I told him about a month ago that I’ll be returning home in a month and we should see each other and that I still have feelings for him. He agreed he wants to see me and he plans on seeing me. That was 3 weeks ago. I’ll be home in 1 week and he said he wants to see me next week.
However, he engages in casual sex. He did before we met and he does now. I don’t know how much but he’s not the type girls throw themselves at. My friend from back home said she saw him on tinder in the stack and it showed recently active. I see him follow random girls from our home town on Instagram like once every couple of weeks, so I assume he’s talking to these girls from the dating apps (don’t argue this please).

My question is, since we’ve been apart for so long and don’t have rules but he knows I want to see him and have feelings for him, and he promised to see me, is him talking to girls online and possibly hooking up a few times before I get home a red flag? Or is this normal guy behavior? Do I turn an eye and stop stalking him and just wait til I get home and see him? Or do I write him off?
Should I excuse his hookup behavior since we aren’t technically dating? Or is it a red flag?
4 Opinion