If your question is that infidlity is a justification for murder or that murder is an inevitable consequence of infidelity then I disagree.

You wouldnt kill someone who cheated on you. There are crimes of passion yes but they are the minority. Many people catch their partners cheating every day without killing them. You have to be quite unstable to take someones life in that situation.

If you are asking wether the partner of a dead person who was known to be cheating comes under suspicion then yes they do. Its probably (I dont know to be sure) one of the biggest motives for murder outside of money, so yes the police would be suspicious.