I love him but what should I do?

My boyfriend of 8 and a half years and I broke up for about 8 months because we we're having relationship problems which turned bitter so I decided I needed a break from it all to gather myself. While on a break he started seeing someone else for about 5 months and she knew about me the whole time and didn't care. After spending time with her and away from me, now he doesn't want her anymore and wants me back but she's having a hard time taking no for an answer. The whole time he was with her I didn't hear from him and no I didn't reach out to him either but when my birthday came the messages started coming from him saying he love me and he misses me and now he wants nothing to do with her.. what should I do?
I love him but what should I do?
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