help! cant seem to finish in bed

My husband and i have always had great sex but lately i cant seem to finish and i dont know why and he's been getting really upset and now thinks im cheating on him when im not. See the only way i can finish is by clitoral stimulation so we tried different positions to shake things up and even used his hands and i just cant seem to get there. this has never happen to me before and its freaking me out. So my question is have you ever went thru this and how did you get over it?