What would you do and do you think it will b okay*?

In my last relationship I suspected my sig other was cheating so I went and got tested. I was clean. then we continued to sleep together for about 3 weeks til we finally broke up. About three weeks later I started sleeping with a very good friend of mine, now my boyfriend who I love very much. Around the time my x and I broke up I noticed I got a wicked uti layer followed by a case of bv and didn't think much of it. Now only four months later I have anorher uti/ bv. So I did some research and stuff like that can b caused by common stds such as chlamydia. To top off my worry I found out my ex did indeed cheat on me w some girl I know in the last few weekends of our relationship. Leaving opportunity for me to b infected if this girl he cheated on me with was a carrier of anything. I brought this up to my current boyfriend so we are going together to get tested this week. He says if I have anything he's going to ume I cheated. He knows the whole story....what else can I do to help him believe me or understand? I'm just heartbroken and need some advice. Thanks in advance