Relationship after cheating

Last year my boyfriend cheated on me and gave me chlamydia, we broke up for alot of reasons at the time but that pushed me to really break up and we spent about a year broken up and barely seeing eachother except to drop of our daughter at eachothers houses.

Then a few months ago I was starting to see alot of improvement in him and we ended up sleeping together and I got pregnant. We decided to take things slow and try again to be together and be a family and he swore he's commited to me again now and that cheating on me last year was the biggest mistake of his life and that he wasnt tempted to do it again.

I took an sti test 2 weeks after the first time back together just to make sure he didn't give me anything again and it came back negative so I thought I was fine.

But then a few month later there was the routine pregnancy sti screening and it came back positive for chlamydia. So obviously I thought he's cheated again but he swore he would have never done that to me again. There is a chance he could have just never been properly treated the first time because he kept forgetting doses of the antibiotics and never went back to get retested to make sure he was clean and then passed it to me again the first time we slept together again and I tested too early for it to catch that it was positive.

Now I'm not sure what to believe because he's been treating me way better than he was when he cheated on me last year so I feel like the behavioural signa of cheating and such arent there but I dont know if I should trust him or not. A big part of me just wants to forgive him and believe him BUT if this ever happened again or if I even thought it happened again I'd dump him really quick with no hesitation.

So after the initial shock and anger I told him I dont want us to be cold and distant with eachother because I'd been really enjoying spending time with him again and being friendly with eachother but that I'm not sure where the relationship is going yet. Somehow he got the idea that I was ok with the whole thing and that I was just gonna completely forgive him with no consequences or anything at all and things would be 100% fine and that kinda makes me mad because even if he actually didnt cheat hes still fucked me over by giving me chlamydia while I'm pregnant.... which is scares me alot and makes me really angry!

So.... if I decide to stay with him.... how can I still be able to communicate to him that this was not ok. I'm really struggling with how to deal with this.... on top of pregnancy stress and other life stress...