Can you get an std form wearing a condom

So I started hooking up with my bd again bc I thought he was single come to find he had a gf the whole time so I went and got checked mind you we used a condom every time but this man gets condoms that are to big for him and both times we hooked up I noticed it was only on the tip to not even mid penis , so our skin was still touching and I notice cum on his skin when I got off of him . Anywayyy my results came back positive and I’m kinda freaking out bc I haven’t had sex with anyone before him for 6 months. I had no symptoms until 3 weeks after having sex with him the first time . Do y’all think it could be from him ? He also told me he hasn’t been with anyone other than his gf and I really don’t think he’s lying about that but who knows . Do y’all think I could’ve got it from him ? And if so by next week if he doesn’t have results should I tell his gf ?

UPDATE : why are y’all coming for me in the comments lol. I feel like I can’t get on this app without feeling stupid we all make mistakes . Yes I slept with him was it my proudest moments no but I had no idea what was going on. I am not being naive just from certain circumstances I don’t think he was trust me I had my doubts .