He's always frustrated with me

This whole week my SO has been frustrated with me. With everything I do and say and idk how else to handle it. I mean we haven't had sex for two and a half weeks and he just begs me for it. The first week I had my period And the second week I just didn't wanna do it . I don't want someone to beg me for sex !!! Why can't it be spontaneous and shit. I feel like I have to be obligated to do it with him because he wants it. I know it's been a while which is probably why he's so angry or all the time.... But anyway we've been fighting and shit and at the end of the fight he's like " I hope you don't leave me and find someone better "