<human>: My boyfriend and I have been going out for about two months and everything is great. We got together really quickly - he asked me to go steady with him five days after meeting him. He is my first serious boyfriend/relationship and he treats me really well; I really couldn't ask for more. He's attentive, kind, doesn't pressure him into doing anything I am uncomfortable with, etc.

The problem is that I know he was in a relationship and broke up with his ex recently - I didn't know the exact date and that it was so recent until I found the date on his Facebook. He got together with his ex in May and we got together in September: that is a four month gap between when he got together with her, broke up with her and got together with me. 

I know he was serious about his ex because I asked him about her and he told me, but he also did mention they were really on and off throughout the entire time. His ex-girlfriend now lives overseas so I'm not worried about them getting back together or anything, and I do trust him. My issue is that now when I'm with him, there is the nagging feeling at the back of my mind that I'm nothing but a rebound and I'm afraid to bring up this issue with him at the moment because if he does tell me I'm the rebound, I don't think I can handle the truth. And even if he denies it, I don't think I'll be able to believe him because of the sheer speed of things.

Am I being paranoid? I'm really afraid this is going to eat away at me because I've never had great self-esteem.

Can you summarize the given text in a few sentences?
<bot>: I'm afraid I'm my boyfriend's rebound girlfriend because of the time it took for him to get together with his ex, break up with her and get together with me (4 months).