Blindesided 😔

I've been dating my current boyfriend for 6 months and he just admitted to me that when we first starting talking around a year ago. He had slept with me and his ex. He doesn't talk to her anymore and we weren't committed at the time. We barely knew each other to be honest we just were co workers, but ended up having a really good chemistry. I've felt a weird vibe between us so I've asked him plenty of times if there is anything he needs to tell me so I'm happy he owned up to it. I'm just pretty upset because he lied. I love him, but I'm just not sure if should stay in this relationship. I'm looking for long term. Is this something you would consider forgivable?