My partner and I have been together 6 months. I am in my mid 20's, and he is early 40s. Both have no children, but I work in childcare, hence I use this site. Usually a lurker, but thought i'd be brave and post 
We get on really well, and I spend 6 nights out of 7 at his house. Before DP met me he had dated a girl. He didn't say how long they were together, but said they'd broken up 3 months before we met. This girl had a baby boy who didn't see his father. This little boy called DP daddy. When they broke up, DP and this girl didn't stay in touch. He said they just drifted apart.
While DP goes out to work, I often stay in his house til I have to go to work. This morning, while in his house, i was looking for a handbag that I had left at his a few months ago, and at the back of his wardrobe, found a carrier bag full of (presumably) his ex and her sons pyjamas. I had a nosy in the bag and there was a prescription and on the prescription said his ex's name and date of birth, which made her to be 21. He's 41! That isn't the problem though. The issue is that he told me when we met that his ex was in her 30's, not her early 20's! Since i've seen his ex's name on the prescription too, i've realised i've seen his exes name in his phonebook on his phone. If they don't keep in touch, i'm wondering why he still has her number?!?! and if he's not in touch with her, why is he keeping the bag of (dirty...eww) baby clothes and his ex's pyjamas?
That isn't the only thing. A couple of months ago I text him around lunchtime to ask him what he was up to. I was at work. He text back saying he was laying on the bed, watching telly. I got home (back to his) that night before him and the bed was still freshly made from when i'd made it in the morning, and the remote that you need to turn the tv on, was still in the spare room from when i'd taken it in there that morning. I didn't confront him about it, because I thought i'd sound like a loon.
Ok, one more thing is that he goes out every other week with his mates. One night DP and I went out to the pub and this woman came up to us and said to him 'didn't I see you last week, weren't you the one I was talking to?' DP said afterwards, without my even asking, that his mates had got talking to a group of people in the pub and she was in the group.
I do get really insecure (been cheated on before in past relationship while pregnant but sadly miscarried) and then he says how much i've changed his life, that he's never cheated before on anyone and how he'd never do it to me or lie to me, but these little things rear their ugly head. When we're together he's a real gentleman, very affectionate and we have a decent sex life. He leaves his phone lying around and i've met all his family who are very nice.