I'm late..

My period is 18 days late I never been this late. Me and my boyfriend been together for almost 4 years on the 29th it will make 4 years. I love him so much but we been fighting lately cause there been rumors he had sex with another girl but he swears it isn't true and he says he is tired of me believing everyone else and not him and I keep accusing him. Even the girl said its not true. Idk what to do he got so mad at me on Friday and changed his number. But today we spoke but he's still mad I don't want to lose him we been together so long but I don't want to chase him either. And if I am pregnant I want him to be supportive like he said he would be. I'm 21 he's 23 almost 24. Any advice ?!