HELP PLEASE!!!! 💔

I told my boyfriend I love him today (I have before more discretely) and he tells me not to love him He probably can't love me because his ex broke his heart, I asked him to promise me he'd let me love him, he said he can't make that promise. we have been dating for four months, do I get out of this now is this a serious red flag?? I'm 19 been in other relationships this is just complicated to me.