AITAH for not wanting to tell my boyfriend I picked up an STD while we weren’t together?

For context, my boyfriend (22) and I (21f) dated for 4 years but broke up on Christmas after I found out he was cheating on me basically all throughout last year. Also TMI but we haven’t had sex since June so when we split, I was honestly really excited to get back out there..

Needless to say by New Years I already had a date with an old friend and HE was the one to initiate the “are you clean” conversation, so I happily sent him any test results I’ve had saved for reassurance. He never sent me proof he was clean, he just said the words and I was so horny that I just believed him. Long story short; He gave me the clap, so I got treated ASAP and tried to reach out but he accused ME of giving it to HIM so I just blocked him.

Now my boyfriend and I got back together on the 19th, and yesterday the guy I met up with had the gall to text me from a spoof and ask why I blocked him. It made me remember our interaction and I wondered if I should tell my boyfriend what I had gotten. It was really eating away at me so I called my sister and she thought I should tell him but when I decided I wasn’t going to told her this, she understood but very bluntly told me she thought it was an asshole thing to do. In my eyes I got treated and made sure not to have relations with anyone else until I came back 100% clean. By the time my boyfriend and I got back together I was clean for two weeks, so why would I tell him something that absolutely will not affect him and might just make him mad at me?? Anyways, I guess I just wanted some outsider perspective and I’m wondering AITHA for not wanting to tell my boyfriend I picked up an STD while we weren’t together?