Boyfriend Cheating!.. Advice Anyone Please

So I recently found out my boyfriend has been cheating on me with his ex that's carrying his second baby. We just recently lost our little one through a miscarriage from a bad car wreck I was in. He's away on business and texts me out the blue he has bad news. Remind you I been to the doctor dealing with the miscarriage. He tells me it's nothing serious but his ex texted him that she has trich and she needs to go get seen. Me and him never use condoms because it's just suppose to be us. I haven't received a call from my doctor about having any sti because I always get checked for those. He's trying to put it on me like I stepped out on him and it's the reason he has it because I told him I don't have it. Should I make another doctors appointment to be rechecked because I don't have any symptoms of what they have. He slept with her while we were on a break I'm so confused and pissed off because that's just putting more stress on me after losing my baby 2 weeks ago. I really don't know what to do or who to turn to about all this stress and depression I've been holding onto. I been trying for almost a year and lost my little baby. How long should I wait ttc my rainbow baby?