Gave me an sti from previous 'relations', should I leave?

When I found out I was pregnant (at 5 weeks) I went to the clinic to get tested for any infection as I got pregnant while me and the baby's dad weren't together and I wanted to be safe. I had nothing. Me and my baby's dad got back together when I was around 16 weeks and been together ever since. I'm now 32 weeks. I've been having alot of yellow discharge for weeks now but i cant remember exactly when it started. I just thought it was because of being pregnant. At 26 weeks i told my midwife and she said its normal. Last week i decided to smell it for the first time and noticed an unpleasant smell. I also had some spotting the other day so I have an appointment to get tested Friday. I honestly don't think he's cheated. Theres just hasnt been a time when he could have. If I have anything, it's from before we got back together and he obviously didn't get himself checked before getting back with me and sleeping with me again. He knows I'm angry I told him how he should have gotten himself checked before getting back with me for the sake of the baby if not himself or me. and all he can say is sorry. I don't know if I definitely have anything yet and I pray to God I'm stressing for nothing but if I do, is this something to leave over? If he cheated I'd be gone no hesitations! But we have been so good since getting back together and are now just waiting on the baby to have our family complete, of course I'm going to be mad at him for days, weeks even because its still his fault for not getting checked knowing im pregnant too. But would you say it's worth throwing it all away for? Would I be a fool for staying even though it is from before we got back together? Honestly have no idea what I should do if the test results are positive!