how fast do you move to different girls?

a guy i’ve liked for abt a month just told me he was talking to someone else which was kind of a punch in the gut. we’re friends and we share music and talk abt movies and stuff but i was kind of waiting for it to become more. so my question is, should i still wait? or should i try to move on. i’ll still have to be friends with him which is why its hard for me to move on. how fast do guys move on from one girl to another? he broke up with his gf of two years, but then like a week later starting like the girl hes talking to rn. idk if this is a red flag or not but i just dont know if i should wait for him or not. advice?