HI people

I have too many things to tell,but I'll try to make it short
So I'm feeling not well but I don't know exact psychological term of what I feel and I call it depression (maybe it's not correct)
I am 31 year old man, I have a five year old daughter.
An year ago my wife left me because of problems we had(we lost 4 day old baby who was born with problems in lungs), and not because of the third person.
A week ago my ex wife called me and suggested to take our daughter to the health resort for a week. I agreed and we went there. during conversation she told me that she is having some hormonal problems because of not having sex for a long time (from the time we drifted apart)
So when I suggested to have a sex, she agreed but said that nothing will change in relationship,just sex and nothing more and we will never live together anymore.
During five days till I was there she was extremly sensitive and great during sex and extremly cold after and before it. We decided to continue our relationship that way but this situation blows my mind. first 2 days of our journey, I was complitly lost, I felt extremly bad, could not sleep at all and I dont know why is that but It's a fact.
In addition she told that she does not see the problem if I have another partner( I dont have) but added that during our sexual relationship she'll
be faithful to me.
What is that???