Me and my partner were together for 6 years, we always drank a lot socially and he did drugs before we got together and very rarely when we were together as I really don’t agree with drugs.
Anyway we had a daughter and I hardly drink at all now but he started drinking more and more and did drugs at our home one night when I was out with friends (our daughter was with her grandparents) I left him over this as it was the last straw for me, we split up for over 6months and he’s drinking and drug habit was a bit out of control but he didn’t drink when he had our daughter. We decided to give things another go a few months ago and things have been OK, he rarely drinks now but I am finding it so hard to trust him and keep wondering if we’re only together for the sake of our daughter although we get on well etc.
But he’s taking our daughter out to the zoo tomorrow with a friend of his (who he used to drink in the pub a lot with) and his son, I can’t help but realise I really don’t trust him and am worried about this. I don’t know if it’s unreasonable as I know he would never put our daughter in danger and they’re going to the zoo so it’s not a drinking type thing but I’m really uneasy and a bit worried about it but I’m not sure if it’s just me being an overprotective mother.
LemonVibe 
Two things:
To me, it sounds like you are with him only for your daughter’s sake. And in that case, I would ask you this:
Is he a good father to her? Is he a good role model? Is he someone you want your daughter to spend a lot of time with and learn from?
If he is a good father, and you believe he’ll be a beneficial presence for your daughter, then by all means, figure out a way to include him in her life. This doesn’t mean, of course, that you have to be with him. It just means that he can be a part of your daughter’s — and by extension, your — life.
If he’s not a good father, though — if he’s not a good presence, then by all means, end this now.