Well ‘complex’ is relative. Complex for me, I should say 
그런데 같이 있다 보니까 터프한 면이 많이 있는 사람이란 걸 알게 됐어요.
The meaning I understand this sentence has is something like:
That being the case, when we saw each other I came to know that this person had many tough aspects (sides to their personality).
The problem is that it doesn’t include anything that should translate as “when”. However it does have “있다 보니까” and I am very unsure why 있다 is conjugated with 다. Furthermore 보니까 I think is more like “because of seeing” but that doesn’t make a whole lot of sense either! You can’t know someone is tough because you saw them?
I’m not sure about the end of the sentence either. I think 사람이란 걸 알게 됐어요 breaks down as:
사람 + 이다 + 라 (as mentioned earlier?) + ㄴ (conjugated for past tense) + 걸 (object of sentence) + 알다 (to know) + 게 되다 (in this case - to come to know)
I write this breakdown because the meaning of the sentence is a little confusing to me, so clearly theres something (perhaps about grammar) which is tripping me up.