is he a cheater ,

so I've fallen head over heels for this guy, this guy makes me unbelibely happy treats me right and don't get me wrong we have had our fights about stupid shit, and he know how in love i am with him and we've talked about having kids and a house together, and all this, before he met me he did sleep around alot which is fine I'm not against that or anything , but anytime I start to let my walls down or become close to him something happens like an ex will message him and I read the conversation and there's nothing there but he doesn't tell me that an ex messaged him, or a girl will start flirting with him and he will kinda flirt back but not overly, and he's had really ruff relationships in the past where girls have hit him, and cheated and made him feel like total shit so idk if he just likes the idea of having a back up plan until we start to get serious and he knows I'm not gonna turn into a crazy women and that he can trust me or i he's just a cheater , we've been together for 6-7 months but if you knew us your hinl years