HELP! Can a guy date and want something serious with a girl, and fuck another girl in the meantime?

My fuckbuddy (guy, 25) of 1 year sort of ended it with me a month ago saying he's started seeing someone seriously. Then 10 days later he hits me up again for a couple of days until I agree to see him again. I ask him if things died out with that other girl, or if he's just being player right now, and he said "yeah, it kinda died out". (I have stalked her on instagram, and it seems like it died out yes.. she deleted the highlights/stories she posted of him).

We fuck 2 times during the next 2-3 weeks.
Yesterday he hit me up again and asked if I could come over at 9, which is where he gets home. I said yes, and at 8:50 he texted me again, saying that he was too tired anyway (he does that sometimes, which is soo annoying).
Today I, for some weird reason, check this girls instagram, and she has posted a story of him again just an hour ago? Apparently they're on a double date with her friend and her friends' boyfriend..

Quite fucked up right? He has always seen other people (for sex) and our agreement is that we can do whatever, but this is so disrespectful to both me and that girl right?

Like is it possible to both be somewhat in love AND fuck somebody else at the same time? Or is he just fucking with her as well?
Updates
+1 y
He texted me if i wanted to come over later today, but I was a pussy and replied "Got work"
Updates
+1 y
Lolthey deleted each other on insta
HELP! Can a guy date and want something serious with a girl, and fuck another girl in the meantime?
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