Any adviceee?

So if you're interested in someone, at that first stage where you're learning things about them and found out this what would you do: he's only had one girlfriend and they were on and off for like 3 years!! He told me they broke up last April but apparently she's bipolar and he had some problems with her saying that he hit her once when he didn't. Would that kinda put you off? That's a really serious relationship they had and I've never actually had one🙈 that 's started to worry me, it's kind of a long time to be with someone... Or am I just being paranoid?