<human>: Can you succinctly summarize the text in 1-3 sentences?

So my ex-fiance (39F) and myself (29M) have decided to split up. We have a one and a half year old daughter together so obviously we're trying to get along for her sake. The relationship had no sex, no affection, romance, emotional connection. Nothing left. Basically we've been just good friends ever since she was pregnant. She admitted to me that she has not had a single sexual thought in the last 2 years. 

The first awkward situation is that we are only 8 months into a 12 month lease and will have to stay here living together for the next 4 months until we can move out into two smaller apartments. Can't afford to keep this place and rent another one for me. We've been managing for the last 6 weeks rather well I guess. 

The real problem I have right now is that I spied on her and I have proof that she has something going on with an ex boyfriend. It looks to have started back up again about 2 months before we broke up. I believe it was mostly for emotional support at the beginning, but I think she's out on a date with him right now. She told me she was going to a movie with a friend but spent way too long getting ready and looked way too dressed up when she left. 

My question is whether or not I should tell her now that I'm aware of him, or just keep it quiet for the sake of sanity. Get through the next 4 months and then get it out in the open once we don't have to live together. I have already written her a letter explaining everything but I can't decide which route to take.
<bot>: Ex-fiance is seeing her ex, has been since before we broke up. We are stuck living together with our daughter for the next 4 months. Should I tell her I know or keep it to myself for now?