What should i do??

Ok.. So me and my ex were engaged for a year and a half. We were trying to have a baby but we broke up at the end of December. He started sleeping with other people so I slept with someone to get back at him. Well i havent had my period sense the week of our brake up. I didn't get my period all last month and last night while I was in the shower I thought I was on my period it was only for the night. I mean I've been cramping for a couple days like my normal period. But I am to nervous to take a test. I think if I am pregnant the dad is the guy I slept with after my ex. But i don't know what to do. I can't be pregnant. Let alone with this guy's kid. Me and my ex started TTC when we got engaged. This would crush him and I can't take care of a baby! Please help me with some advice.